We present some of the diversity of functional, biologically relevant, enzymatic filament structures. The recent advances in CryoEM and associated structural computational methods, coupled with whole genome screens, have helped identify and recognize these oligomers as important in different areas such as regulation, activation, selectivity, and substrate channeling.

Viroporins are small viral ion channels that play important roles in the viral infection cycle and are proven antiviral drug targets. Matrix protein 2 from influenza A (AM2) is the best-characterized viroporin, and the current paradigm is that AM2 forms monodisperse tetramers. Here, we used native mass spectrometry and other techniques to characterize the oligomeric state of both the full-length and transmembrane (TM) domain of AM2 in a variety of different pH and detergent conditions. Unexpectedly, we discovered that AM2 formed a range of different oligomeric complexes that were strongly influenced by the local chemical environment. Native mass spectrometry of AM2 in nanodiscs with different lipids showed that lipids also affected the oligomeric states of AM2. Finally, nanodiscs uniquely enabled the measurement of amantadine binding stoichiometries to AM2 in the intact lipid bilayer. These unexpected results reveal that AM2 can form a wider range of oligomeric states than previously thought possible, which may provide new potential mechanisms of influenza pathology and pharmacology.

We present some preliminary protocols for coupled reaction assays. Students are asked to move from direct activity assays using alkaline phosphatase (AP) and para‐nitrophenolphosphate into coupled reaction systems. We study phosphofructokinase (PFK) with a coupled reaction assay. To segue from AP to PFK, we spend one lab period trying to force AP to catalyze the reverse reaction and discuss energetics and Le Chatelier’s principle. The concept of reversibility of a reaction and the role of the enzyme as a catalyst for both the forward and reverse reaction is discussed. This lays the groundwork for using the popular pyruvate kinase, lactate dehydrogenase coupled reaction system for measuring the rate of ATP hydrolysis for many enzyme systems including that of our final project, PFK.

It is well known the dimerization state of receptor tyrosine kinases (RTKs), in conjunction with binding partners such as the growth factor receptor bound protein 7 (Grb7) protein, plays an important role in cell signaling regulation. Previously, we proposed, downstream of RTKs, that the phosphorylation state of Grb7SH2 domain tyrosine residues could control Grb7 dimerization, and dimerization may be an important regulatory step in Grb7 binding to RTKs. In this manner, additional dimerization‐dependent regulation could occur downstream of the membrane‐bound kinase in RTK‐mediated signaling pathways. Extrapolation to the full‐length (FL) Grb7 protein, and the ability to test this hypothesis further, has been hampered by the availability of large quantities of pure and stable FL protein. Here, we report the biophysical characterization of the FL Grb7 protein and also a mutant representing a tyrosine‐phosphorylated Grb7 protein form. Through size exclusion chromatography and analytical ultracentrifugation, we show the phosphorylated‐tyrosine‐mimic Y492E‐FL‐Grb7 protein (Y492E‐FL‐Grb7) is essentially monomeric at expected physiological concentrations. It has been shown previously the wild‐type FL Grb7(WT‐FLGrb7) protein is dimeric with a dissociation constant (Kd) of approximately 11μM. Our studies here measure a FL protein dimerization Kd of WT‐FL‐Grb7 within one order of magnitude at approximately 1μM. The approximate size and shape of the WT‐FL‐Grb7 in comparison the tyrosine‐phosphorylation mimic Y492E‐FL‐Grb7 protein was determined by dynamic light scattering methods. In vitro phosphorylation of the Grb7SH2 domain indicates only one of the available tyrosine residues is phosphorylated, suggesting the same phosphorylation pattern could be relevant in the FL protein. The biophysical characterization studies in total are interpreted with a view towards understanding the functionally active Grb7 protein conformation.

Filament or run-on oligomer (ROO) formation by enzymes is now recognized as a widespread phenomenon with potentially unique enzyme regulatory properties and biological roles. SgrAI is an allosteric type II restriction endonuclease that cleaves two types of sites, primary and secondary, but cleaves secondary only in the presence of primary. Primary site DNA activates SgrAI to form ROO with rapid DNA cleavage activity and that can incorporate SgrAI/DNA complexes containing secondary site DNA, thereby inducing their cleavage. Structural methods including x-ray crystallography and cryo-electron microscopy have been used to characterize the three-dimensional structure of the ROO of SgrAI bound to DNA. These structures, combined with kinetic FRET measurements of the DNA cleavage reaction, have been used in global modeling and data fitting to derive microscopic rate constants and investigate cooperativity, growth mechanisms, product trapping and to compare to conventional, non-run on oligomer mechanisms. Mutations which disrupt the ROO were tested in vivo for anti-phage activity. The three-dimensional structure of SgrAI bound to primary site DNA and in the run-on oligomer form shows a left-handed helix with 4 SgrAI/DNA complexes per turn, and that could in principle extend indefinitely. Global model data fitting and the derived rate constants show that association of SgrAI/DNA complexes into the run-on oligomer is rate limiting and is also the feature of the mechanism responsible for sequestering activated DNA cleavage of primary and secondary sites on the same DNA molecule as the activating sequences (a.k.a. the primary site sequences). This analysis also shows that only very limited product trapping occurs, and that the run-on oligomers are not limited to dissociating and growing from only the ends. DNA cleavage was found to be ten-fold faster than ROO dissociation, providing a commitment to the enzyme reaction pathway. Finally, simulations with the models and derived rate constants show that the SgrAI run-on oligomer mechanism is advantageous over the conventional, non-run on oligomer mechanism in both speed and sequestration of activated DNA cleavage, particularly in cleavage of secondary sites, not protected by methylation on the host genome. Mutations which reduce ROO formation completely abolish the anti-phage activity of SgrAI in vivo, showing the critical role of filament formation to biological function. Support or Funding Information This work was supported by NSF MCB-1410355 This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Here, we investigate an unusual antiviral mechanism developed in the bacterium Streptomyces griseus SgrAI is a type II restriction endonuclease that forms run-on oligomer filaments when activated and possesses both accelerated DNA cleavage activity and expanded DNA sequence specificity. Mutations disrupting the run-on oligomer filament eliminate the robust antiphage activity of wild-type SgrAI, and the observation that even relatively modest disruptions completely abolish this anti-viral activity shows that the greater speed imparted by the run-on oligomer filament mechanism is critical to its biological function. Simulations of DNA cleavage by SgrAI uncover the origins of the kinetic advantage of this newly described mechanism of enzyme regulation over more conventional mechanisms, as well as the origin of the sequestering effect responsible for the protection of the host genome against damaging DNA cleavage activity of activated SgrAI.IMPORTANCE This work is motivated by an interest in understanding the characteristics and advantages of a relatively newly discovered enzyme mechanism involving filament formation. SgrAI is an enzyme responsible for protecting against viral infections in its host bacterium and was one of the first such enzymes shown to utilize such a mechanism. In this work, filament formation by SgrAI is disrupted, and the effects on the speed of the purified enzyme as well as its function in cells are measured. It was found that even small disruptions, which weaken but do not destroy filament formation, eliminate the ability of SgrAI to protect cells from viral infection, its normal biological function. Simulations of enzyme activity were also performed and show how filament formation can greatly speed up an enzyme's activation compared to that of other known mechanisms, as well as to better localize its action to molecules of interest, such as invading phage DNA.

We describe our continuing efforts to evolve a self‐directed, discovery based biochemical research laboratory curricula. As a required course for biochemistry undergraduate degrees, we emphasize science writing and literature review as well as molecular graphics and strucure‐function analysis. A challenge comes from training inexperienced students to become accomplished, troubleshooting scientists. The lab course provides instruction in scientific writing, as well as in the design, execution, and interpretation of biochemical research projects. The first goal is to train students in reading and understanding original peer‐reviewed scientific reports, as well as in writing in a scientific style (i.e. following Biochemistry format). The second goal is to bridge the gap between receiving detailed lab protocols and the ability to design, implement, troubleshoot and communicate protein based biochemical research investigations in small groups. Our efforts to develop and evolve this course in a land‐grant university are detailed here.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Filament formation by non-cytoskeletal enzymes has been known for decades, yet only relatively recently has its wide-spread role in enzyme regulation and biology come to be appreciated. This comprehensive review summarizes what is known for each enzyme confirmed to form filamentous structures in vitro , and for the many that are known only to form large self-assemblies within cells. For some enzymes, studies describing both the in vitro filamentous structures and cellular self-assembly formation are also known and described. Special attention is paid to the detailed structures of each type of enzyme filament, as well as the roles the structures play in enzyme regulation and in biology. Where it is known or hypothesized, the advantages conferred by enzyme filamentation are reviewed. Finally, the similarities, differences, and comparison to the SgrAI endonuclease system are also highlighted.

Enzyme filaments are defined as reversible, functional, linear self-assemblies of a single type of enzyme. Filamentation has recently emerged as a new mode of enzymatic regulation. In this Comment, we briefly introduce the diversity and functional consequences of enzyme filamentation.

Filament or run-on oligomer formation by metabolic enzymes is now recognized as a widespread phenomenon having potentially unique enzyme regulatory properties and biological roles, and its dysfunction is implicated in human diseases such as cancer, diabetes, and developmental disorders. SgrAI is a bacterial allosteric type II restriction endonuclease that binds to invading phage DNA, may protect the host DNA from off-target cleavage activity, and forms run-on oligomeric filaments with enhanced DNA-cleavage activity and altered DNA sequence specificity. However, the mechanisms of SgrAI filament growth, cooperativity in filament formation, sequestration of enzyme activity, and advantages over other filament mechanisms remain unknown. In this first of a two-part series, we developed methods and models to derive association and dissociation rate constants of DNA-bound SgrAI in run-on oligomers and addressed the specific questions of cooperativity and filament growth mechanisms. We show that the derived rate constants are consistent with the run-on oligomer sizes determined by EM analysis and are most consistent with a noncooperative growth mode of the run-on oligomer. These models and methods are extended in the accompanying article to include the full DNA-cleavage pathway and address specific questions related to the run-on oligomer mechanism including the sequestration of DNA-cleavage activity and trapping of products.

Efforts to establish an upper division lab course based on self‐directed, discovery based biochemical research are detailed. Consideration of the varying student backgrounds and levels of preparation must be balanced with preparation for the departmental requirement of a laboratory based senior thesis. The major goals of this lab course are to provide instruction in scientific writing, as well as in the design, execution, and interpretation of biochemical research projects. The first goal is to train students in reading and understanding original peer‐reviewed scientific reports, as well as in writing in a scientific style (i.e. following Biochemistry format). The second goal is to bridge the gap between receiving detailed lab protocols and the ability to design, implement, troubleshoot and communicate protein based biochemical research investigations in small groups. Our efforts to develop and evolve this course in a land‐grant university are detailed here.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Protein-based self-assembled nanostructures hold tremendous promise as smart materials. One strategy to control the assembly of individual protein modules takes advantage of the directionality and high affinity bonding afforded by metal chelation. Here, we describe the use of 2,2'-bipyridine units (Bpy) as side chains to template the assembly of large structures (MW approx. 35 000 Da) in a metal-dependent manner. The structures are trimers of independently folded 3-helix bundles, and are held together by 2 Me(Bpy)3 complexes. The assemblies are stable to thermal denaturation, and are more than 90% helical at 90°C. Circular dichroism spectroscopy shows that one of the 2 possible (Bpy)3 enantiomers is favored over the other. Because of the sequence pliability of the starting peptides, these constructs could find use to organize functional groups at controlled positions within a supramolecular assembly.

Filament or run-on oligomer formation by enzymes is now recognized as a widespread phenomenon with potentially unique enzyme regulatory properties and biological roles. SgrAI is an allosteric type II restriction endonuclease that forms run-on oligomeric filaments with activated DNA cleavage activity and altered DNA sequence specificity. In this two-part work, we measure individual steps in the run-on oligomer filament mechanism to address specific questions of cooperativity, trapping, filament growth mechanisms, and sequestration of activity using fluorophore-labeled DNA, kinetic FRET measurements, and reaction modeling with global data fitting. The final models and rate constants show that the assembly step involving association of SgrAI-DNA complexes into the run-on oligomer filament is relatively slow (3-4 orders of magnitude slower than diffusion limited) and rate-limiting at low to moderate concentrations of SgrAI-DNA. The disassembly step involving dissociation of complexes of SgrAI-DNA from each other in the run-on oligomer filament is the next slowest step but is fast enough to limit the residence time of any one copy of SgrAI or DNA within the dynamic filament. Further, the rate constant for DNA cleavage is found to be 4 orders of magnitude faster in the run-on oligomer filament than in isolated SgrAI-DNA complexes and faster than dissociation of SgrAI-DNA complexes from the run-on oligomer filament, making the reaction efficient in that each association into the filament likely leads to DNA cleavage before filament dissociation.

Analytical ultracentrifugation (AUC) is a first principles based method to determine absolute sedimentation coefficients and buoyant molar masses of macromolecules and their complexes, reporting on their size and shape in free solution. The purpose of this multi-laboratory study was to establish the precision and accuracy of basic data dimensions in AUC and validate previously proposed calibration techniques. Three kits of AUC cell assemblies containing radial and temperature calibration tools and a bovine serum albumin (BSA) reference sample were shared among 67 laboratories, generating 129 comprehensive data sets. These allowed for an assessment of many parameters of instrument performance, including accuracy of the reported scan time after the start of centrifugation, the accuracy of the temperature calibration, and the accuracy of the radial magnification. The range of sedimentation coefficients obtained for BSA monomer in different instruments and using different optical systems was from 3.655 S to 4.949 S, with a mean and standard deviation of (4.304 ± 0.188) S (4.4%). After the combined application of correction factors derived from the external calibration references for elapsed time, scan velocity, temperature, and radial magnification, the range of s-values was reduced 7-fold with a mean of 4.325 S and a 6-fold reduced standard deviation of ± 0.030 S (0.7%). In addition, the large data set provided an opportunity to determine the instrument-to-instrument variation of the absolute radial positions reported in the scan files, the precision of photometric or refractometric signal magnitudes, and the precision of the calculated apparent molar mass of BSA monomer and the fraction of BSA dimers. These results highlight the necessity and effectiveness of independent calibration of basic AUC data dimensions for reliable quantitative studies.

SgrAI is a type II restriction endonuclease with an unusual mechanism of activation involving run-on oligomerization. The run-on oligomer is formed from complexes of SgrAI bound to DNA containing its 8 bp primary recognition sequence (uncleaved or cleaved), and also binds (and thereby activates for DNA cleavage) complexes of SgrAI bound to secondary site DNA sequences which contain a single base substitution in either the 1st/8th or the 2nd/7th position of the primary recognition sequence. This modulation of enzyme activity via run-on oligomerization is a newly appreciated phenomenon that has been shown for a small but increasing number of enzymes. One outstanding question regarding the mechanistic model for SgrAI is whether or not the activating primary site DNA must be cleaved by SgrAI prior to inducing activation. Herein we show that an uncleavable primary site DNA containing a 3'-S-phosphorothiolate is in fact able to induce activation. In addition, we now show that cleavage of secondary site DNA can be activated to nearly the same degree as primary, provided a sufficient number of flanking base pairs are present. We also show differences in activation and cleavage of the two types of secondary site, and that effects of selected single site substitutions in SgrAI, as well as measured collisional cross-sections from previous work, are consistent with the cryo-electron microscopy model for the run-on activated oligomer of SgrAI bound to DNA.

ABSTRACTDNA repair is fundamental to genome stability and is found in all three domains of life. However many archaeal species, such as Methanopyrus kandleri, contain only a subset of the eukaryotic nucleotide excision repair (NER) homologs, and those present often contain significant differences compared to their eukaryotic homologs. To clarify the role of the NER XPG‐like protein Mk0566 from M. kandleri, its biochemical activity and three‐dimensional structure were investigated. Both were found to be more similar to human FEN‐1 than human XPG, suggesting a biological role in replication and long‐patch base excision repair rather than in NER. Proteins 2015; 83:188–194. © 2014 Wiley Periodicals, Inc.