An extract from the obituary for Sir Lawrence Bragg by M. F. Perutz [Nature (London), (1971), 233, 74-76] is given.

Erwin Schrödinger's book What is Life?, published in 1944, drew several of the brightest physicists into molecular biology. But the book's chief merit lies in its rescue from obscurity and popularization of an earlier paper by Timoféeff, Zimmer and Delbrück.

The low oxygen affinity of many fish haemoglobins at low pH is suggested to be due to the replacement by serine of the reactive cysteine F9β found in mammalian haemoglobins. Model building shows that hydrogen bonds between this serine and the C-terminal histidine stabilize the quaternary deoxy(T) structure. A stereochemical model for the binding of the allosteric effectors ATP or GTP is also advanced.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTInteractions between the quaternary structure of the globin and the spin state of the heme in ferric mixed spin derivatives of hemoglobinMax F. Perutz, Jeremy K. M. Sanders, David H. Chenery, Robert W. Noble, Russell R. Pennelly, Leslie W. M. Fung, Chien Ho, Ivo Giannini, Dietmar Poerschke, and Heinz WinklerCite this: Biochemistry 1978, 17, 17, 3640–3652Publication Date (Print):August 22, 1978Publication History Published online1 May 2002Published inissue 22 August 1978https://pubs.acs.org/doi/10.1021/bi00610a034https://doi.org/10.1021/bi00610a034research-articleACS PublicationsRequest reuse permissionsArticle Views160Altmetric-Citations84LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts

William Henry Bragg, 1862–1942: Man and Scientist. By G. M. Caroe. (Cambridge University Press: Cambridge and London, 1978.) £8.95.

Electrostatic effects dominate many aspects of protein behavior. When polypeptide chains fold up, most polar side chains seek the exterior, where they can be solvated. Water bound in the interior has been found between the domains of enzymes of the chymotrypsin family, and between the subunits of hemoglobin and tobacco mosaic virus protein. Assembly of this protein from disk to virus is triggered by electrostatic interactions between neighboring subunits. Lysozyme stabilizes the constellation of charges involved in the transition state of its substrate by both permanent and induced dipoles. All factors that lower the oxygen affinity of hemoglobin act by strengthening the salt bridges that constrain its quaternary deoxy (T) structure. Enzymes of thermophile bacteria owe their extra stability mostly to additional salt bridges. The rate of denaturation of hemoglobins by alkali is determined by the ionization of internal side chains with pK 's of about 12.

Human fluoromethaemoglobin with inositol hexaphosphate (IHP) in 0.05 m-phosphate buffer was crystallized by addition of polyethylene glycol (PEG). The crystals are isomorphous with those of deoxyhaemoglobin A without IHP grown in solutions containing PEG by Ward et al. (1975). The structure was investigated by means of a difference Fourier synthesis against deoxyhaemoglobin A based on X-ray data collected within a limiting sphere of 3.5 Å−1. The four subunits are arranged in the quaternary T structure and IHP is bound at the same site between the β chains as in deoxyhaemoglobin. In both the α and β haem regions the distance between the haem plane and the F helix is reduced in fluoromethaemoglobin relative to deoxyhaemoglobin and the iron atom is moved from the proximal towards the distal side of the plane, but the change, if any, in the distance between the iron and the Nε of the proximal histidine cannot be clearly established. The α Fe in fluoromethaemoglobin is either in the haem plane or up to 0.8 Å on the distal side, suggesting the possibility of rupture of the bond to the histidines Nε; it was not possible to estimate the position of the β iron. The main spectral changes associated with the reaction of fluoromethaemoglobin with IHP take place in less than 3 ms at room temperature.

The structure of horse methaemoglobin has been redetermined by phase extension and refinement. This has improved our knowledge of the haem geometry and the stereochemistry of the interfaces between the subunits, and confirmed the disorder of the C-terminal residues. Using new four-circle diffractometer data between the limiting spheres of radius 10 and 2.0 Å−1, the co-ordinates determined by Perutz et al. (1968a,b) were subjected to successive cycles of real-space refinement into electron density maps calculated with observed ¦F¦ values and phases derived from the latest refined model, until the reliability index had dropped from an initial value of 0.45 to 0.23. The positions of the iron atoms relative to the planes of the porphyrin rings were refined separately, and checked by Fourier syntheses based on anomalous scattering and by difference Fourier syntheses calculated with coefficients from which the iron contributions had been removed. The general root-mean-squared error in atomic positions is 0.32 Å; the probable error in the displacement of the iron atoms from the porphyrin planes is 0.06 Å. The difference Fourier synthesis, obtained after refinement of the protein was complete, showed 41 bound water molecules per asymmetric unit and also revealed five errors in amino acid sequence, one of which was confirmed chemically.

The structure of human foetal deoxyhaemoglobin FII has been solved at a resolution of 2·5 Å. Phase angles were determined by a single isomorphous replacement with paramercuribenzoate combined with the molecular replacement method, using the atomic co-ordinates of deoxyHbA determined by Fermi (1975). A difference Fourier electron density map of deoxyHbF—A is largely featureless except where the amino acid sequences of the two proteins differ, and at positions occupied by bound solvent molecules which were not included in the phase calculations. These occur in the same positions between neighbouring subunits as in deoxyHbA. The only detectable differences between the tertiary structures of the β and γ-chains occur in the two N-terminal segments. In the γ-chain the NA segment is further from the EF segment and from the H helix, and the A helix is closer to the E helix than in the β-chains. As a result of the former change, an anion bound between Vallβ and Lys82β in deoxyHbA is absent from deoxyHbF, and the distances from the two phosphate groups of 2,3-diphosphoglycerate to Hienβ may be increased in deoxyHbF, which may contribute to the lower affinity of foetal deoxyHbF for 2,3-diphosphoglycerate. The reduction of the distance between helices A and E is similar to that which occurs in deoxyhaemoglobin on addition of organic phosphates, where it apparently tightens up the structure and lowers its intrinsic oxygen affinity. It may be responsible for the lower oxygen affinity of “stripped” haemoglobin F compared to A. Although deoxyHbA and F crystallize in different space groups, both crystals are made up of filaments of molecules stacked parallel to the molecular X-axis. The intermolecular contacts between neighbouring molecules along the filament are the same except for the weakening of one electrostatic interaction which may contribute to the higher solubility of deoxyHbF, and to its antisickling effect.

The structure is based on a difference Fourier synthesis at 2.8 Å resolution, using observed structure amplitudes and calculated phases, derived from a refinement of horse methaemoglobin at 2.0 Å resolution. Carbonmonoxyhaemoglobin has the same quaternary structure as methaemoglobin, but differs from it by slight changes in tertiary structure in the immediate vicinity of the haems. On transition from met- to carbonmonoxyhaemoglobin the distal histidines move away from the haem ligands towards the molecular surface, and both the haems and F-helices rotate slightly and shift towards the distal side. In methaemoglobin the sulphydryl group of cysteine F9(93)β is in equilibrium between two alternative positions: one external and the other half-buried in the “tyrosine pocket” between helices F and H. In carbonmonoxyhaemoglobin all the electron density for the sulphydryl group is in the half-buried position, so that the side chain of tyrosine HC2(145)β is completely displaced from its pocket. The difference map shows that the CO oxygen lies off the haem axis in both subunits, but the carbon cannot be seen as it coincides with the water molecule in methaemoglobin. A preliminary refinement of carbonmonoxyhaemoglobin suggests that the carbon may be displaced from the haem axis in the same direction as the oxygen. The haem pocket is so constructed that it fits an oxygen molecule in the bent conformation, but not a CO molecule which has its axis normal to the haem plane, because of steric hindrance by Nϵ of the distal histidine and by Cγ2 of the distal valine. These two side chains apparently push the CO oxygen off the haem axis. The difference map indicates that in methaemoglobin the α-haem is ruffled and that on transition from met- to carbonmonoxyhaemoglobin it becomes flattened; in the β-haem the iron appears to move towards the porphyrin plane. The resolution is not sufficient to determine the exact position of the iron atoms and the proximal histidines relative to the porphyrins.

Any research which has shed light on the nature of disease or opened new ways to its prevention or cure is here termed relevant, and the question will be asked whether the research could have been planned with these aims in mind. Examples will be taken from the chemistry and X-ray analysis of proteins and from molecular genetics. Blow and Hartley determined the amino acid sequence and atomic structure of the digestive enzyme chymotrypsin in order to solve the problem of enzymic catalysis. They succeeded but what they found has proved to be of much wider improtance than could have been foreseen at the outset: it gives the key to the mechanism of blood clotting and suggests new methods for its control. X-ray analysis of haemoglobin was started at a time when the structure of proteins was regarded as the central problem of biology, but it did not seem likely then that the results would shed light on the molecular pathology of inherited diseases. Ames made a life-long study of the genetic control of histidine biosynthesis in Salmonella because it represents an example of a widely used biological mechanism, but without expecting it to have any practical applications. Yet his recent exploitation of the system for the rapid and sensitive detection of chemical carcinogens may represent a breakthrough in cancer prevention. This unpredictable relationship of molecular biology to medicine is symptomatic of the subject's youth.

MOST enzymes are quickly inactivated above about 55 °C but those from thermophile bacteria are stable for long periods at higher temperatures1. We do not know why because so far their structures have proved too complex. For example although the tertiary and quaternary structures of the enzyme glyceraldehyde phosphate dehydrogenase from lobster muscle and from Bacterium stearothermophilus are alike their amino acid sequences differ by more than 130 out of some 330 positions which makes it hard to decide why the stearothermophilus enzyme is more stable. The electron transfer protein ferredoxin offers a better chance because its single polypeptide chain contains fewer than 60 residues; its structure is known and its heat stability and amino acid sequence have been determined in both mesophile and thermophile bacteria. We have built an atomic model of this protein, replaced its amino acid side chains in turn to correspond to the published sequences and searched for possible causes of the greater heat stability of ferredoxins from thermophile bacteria. We found that it arises mainly from external salt bridges linking residues near the amino terminus to others near the carboxy terminus. Haemoglobin A2 a minor fraction of adult human haemoglobin which is a little more heat stable than the major fraction, haemoglobin A, seemed another good choice because its amino acid sequence differs from that of A at only 10 positions. The atomic model suggests that at only two of these positions are the replacements likely to contribute to the extra stability of haemoglobin A2 one replacement providing an extra hydrogen bond between the α1 and β1 subunits and the other adding two non-polar interactions to a surface crevice within the β subunits. To account for the increased heat stability of the two proteins the extra bond energy provided by these interactions need not be larger than 10 kJ for ferredoxin or 5 kJ for haemoglobin A2.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTInfluence of globin structure on the state of the heme. III. Changes in heme spectra accompanying allosteric transitions in methemoglobin and their implications for heme-heme interactionMax F. Perutz, Elizabeth J. Heidner, Jane E. Ladner, John G. Beetlestone, Chien Ho, and Edward F. SladeCite this: Biochemistry 1974, 13, 10, 2187–2200Publication Date (Print):May 1, 1974Publication History Published online1 May 2002Published inissue 1 May 1974https://pubs.acs.org/doi/10.1021/bi00707a028https://doi.org/10.1021/bi00707a028research-articleACS PublicationsRequest reuse permissionsArticle Views254Altmetric-Citations140LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTInfluence of globin structure on the state of the heme. I. Human deoxyhemoglobinMax F. Perutz, Jane E. Ladner, Sanford R. Simon, and Chien HoCite this: Biochemistry 1974, 13, 10, 2163–2173Publication Date (Print):May 1, 1974Publication History Published online1 May 2002Published inissue 1 May 1974https://pubs.acs.org/doi/10.1021/bi00707a026https://doi.org/10.1021/bi00707a026research-articleACS PublicationsRequest reuse permissionsArticle Views563Altmetric-Citations225LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts

D-2,3-DIPHOSPHOGLYCERATE (DPG) facilitates the transfer of oxygen from human red blood cells to the tissues by lowering the oxygen affinity of haemoglobin1. It does so by combining preferentially with one of the two alternative forms of haemoglobin, namely the deoxy form, in the ratio of 1 mol per mol tetramer. Its binding site was predicted from biochemical and model building experiments and then determined directly by X-ray crystallography2. The site lies at the entrance to the central cavity between the N-termini of the β chains and is surrounded by four pairs of basic groups: the α amino group of valine 1 and the side chains of histidines 2 and 143, and of lysine 82. The basic groups are related in pairs by the molecular dyad and arranged so as to complement the acidic groups of DPG by forming seven salt bridges (Fig. 1). On oxygenation the N-termini of the β chains move apart and the cavity closes up so that the stereochemical complementarity is lost3. Oxyhaemoglobin does also bind DPG, but much more weakly, and the binding site is still unknown.