The tetracycline class of antibiotics is widely used for treating bacterial diseases including Lyme disease, anthrax, acne vulgaris, and pneumonia. Using a series of high-resolution cryo-electron microscopy (cryo-EM) structures, we show that tetracyclines can simultaneously target the mRNA decoding center in the 30S subunit and the nascent peptide exit tunnel (NPET) in the 50S subunit of the bacterial ribosome. Among the tested tetracyclines, Doxycycline was distinct in its ability to dimerize and bind the NPET at multiple locations. Structural comparison of Doxycycline, Minocycline, and Sarecycline bound to the Escherichia coli and Cutibacterium acnes 70S ribosome revealed species-specific differences affecting drug interaction and occupancy. Our results reveal a dual site mechanism of action for tetracyclines and provide a structural basis for rational design of narrow spectrum tetracyclines to overcome the rising threat of antibiotic resistance.

Deucravacitinib, 6-(cyclopropanecarbonylamido)-4-[2-methoxy-3-(1-methyl-1,2,4-triazol-3-yl)anilino]-N-(trideuteriomethyl)pyridazine-3-carboxamide, is a highly selective inhibitor of protein tyrosine kinase 2 (TYK2) that targets the Janus kinase (JAK)-signal transducer and activator of transcription (STAT) pathway. The structural basis for its selectivity and allosteric inhibition remains poorly understood. Here, we investigate the inhibition mechanism through analysis of available structures relevant to the STAT pathway, including crystal structures of the truncated TYK2 FERM-SH2 domain bound to the IFNα type I receptor (IFNαR1) and the truncated TYK2 JH2-JH1 domain. Our computational analysis provides a mechanistic hypothesis for the relatively rapid interferon-induced gene expression mediated by TYK2 relative to other cytokines. We find that deucravacitinib inhibits TYK2 kinase in three distinct states: the autoinhibited state and two activated states for autophosphorylation and phosphorylation of downstream protein substrates. Its binding to the TYK2 pseudokinase domain in the autoinhibited state restricts the essential dynamics of the TYK2 kinase domain required for kinase activity. Furthermore, it binds competitively with ATP in the pseudokinase domain, and also directly prevents formation of the active state of TYK2 through steric clashes.

Comprehensive in situ structures of macromolecules can transform our understanding of biology and advance human health. Here, we map protein synthesis inside human cells in detail by combining automated cryo-focused ion beam (FIB) milling and in situ single-particle cryo electron microscopy (cryo-EM). With this in situ cryo-EM approach, we resolved a 2.2 Å consensus structure of the human 80S ribosome and unveiled 23 functional states, nearly all better than 3 Å resolution. Compared to in vitro studies, we observed variations in ribosome structures, distinct environments of ion and polyamine binding, and associated proteins such as EDF1 and NACβ that are typically not enriched with purified ribosomes. We also detected additional peptide-related density features on the ribosome and visualized ribosome-ribosome interactions in helical polysomes. Finally, high-resolution structures from cells treated with homoharringtonine and cycloheximide revealed a distinct translational landscape and a spermidine that interacts with cycloheximide at the E site, one of the numerous polyamines that also bind native ribosomes. These results underscore the value of high-resolution in situ studies in the native environment.

The tetracycline class of antibiotics is widely used for treating bacterial diseases including Lyme disease, anthrax, acne vulgaris, and pneumonia. Using a series of high-resolution cryo-electron microscopy (cryo-EM) structures, we show that tetracyclines can simultaneously target the mRNA decoding center and the nascent peptide exit tunnel (NPET) of the bacterial 70S ribosome. Among the tested tetracyclines, Doxycycline was unique in its ability to dimerize and bind the NPET at multiple locations. Structural comparison of Doxycycline, Minocycline, and Sarecycline bound to the Escherichia coli and Cutibacterium acnes 70S ribosome revealed species-specific differences affecting drug interaction and occupancy. Our results redefine the mechanism of action for tetracyclines and provide a structural basis for rational design of narrow spectrum tetracyclines to overcome the rising threat of antibiotic resistance. ### Competing Interest Statement CGB has served as an investigator and/or consultant for Almirall, Ortho Dermatologics, Sun Pharma, and Teladoc.

BACKGROUND:Epidermal differentiation disorders [EDDs; ichthyosis and palmoplantar keratoderma (PPK)] are heritable skin conditions characterized by localized or generalized skin scaling and erythema. OBJECTIVES:To identify novel genetic variants that cause PPK and progressive symmetric erythrokeratoderma (PSEK) phenotypes. METHODS:We performed whole-exome sequencing in a large cohort of people with EDD, including PPK and PSEK phenotypes, to identify novel genetic variants. We investigated the variant consequence using in silico predictions, assays in patient keratinocytes, high-resolution spatial transcriptomics and quantitative cytokine profiling. RESULTS:We identified three unrelated kindreds with autosomal dominant transmission of heterozygous SLURP1 variants affecting the same amino acid within the signal peptide (c.65C > A, p.A22D and c.65C > T, p.A22V). One (p.A22V) had isolated PPK; the other two (p.A22D) had PSEK and PPK. In silico modelling suggested that both variants alter pro-SLURP1 cleavage, appending two amino acids to the secreted protein, which we subsequently confirmed with mass spectrometry. In patient keratinocytes we found increased differentiation-induced SLURP1 expression and secretion compared to healthy control cells. Spatial transcriptomics revealed increased nuclear factor-κB (NF-κB) signalling and innate immune activity, which may contribute to epidermal hyperproliferation in dominant SLURP1-PPK/PSEK. CONCLUSIONS:Our results expand the phenotypic spectrum of EDD due to SLURP1 pathogenic variants. While autosomal recessive Mal de Meleda is due to biallelic loss-of-function SLURP1 variants, our finding of autosomal dominant SLURP1 pathogenic variants in kindreds with PPK and PSEK suggests a novel mechanism of action. We found that heterozygous p.A22V and p.A22D SLURP1 variants append two amino acids to secreted SLURP1, increase differentiation-induced SLURP1 expression and secretion and upregulate NF-κB signalling in people with PSEK.

Cryogenic electron microscopy (cryo-EM) and cryogenic electron tomography allow determination of structures of biological macromolecules in their native state in solution at atomic or near-atomic resolution. Recent advances in cryo-EM, that is, the “resolution revolution,” and the establishment of national centers for cryo-EM data collection have remarkably expanded its applicability to practically all areas of health-related research. In this methods review, we highlighted the basics of single-particle cryo-EM and its application in the research of macromolecules and macromolecular complexes related to dermatology. We further illustrated a few examples of how this approach can be incorporated into drug development and study.

Clindamycin is a highly effective antibiotic of the lincosamide class. It has been widely used for decades to treat a range of skin and soft tissue infections in dermatology and medicine. Clindamycin is commonly prescribed for acne vulgaris, with current practice standards utilizing fixed-combination topicals containing clindamycin that prevent Cutibacterium acnes growth and reduce inflammation associated with acne lesion formation. Certain clinical presentations of folliculitis, rosacea, staphylococcal infections, and hidradenitis suppurativa are also responsive to clindamycin, demonstrating its suitability and versatility as a treatment option. This review describes the use of clindamycin in dermatological practice, the mechanism of protein synthesis inhibition by clindamycin at the level of the bacterial ribosome, and clindamycin’s anti-inflammatory properties with a focus on its ability to ameliorate inflammation in acne. A comparison of the dermatologic indications for similarly utilized antibiotics, like the tetracycline class antibiotics, is also presented. Finally, this review addresses both the trends and mechanisms for clindamycin and antibiotic resistance, as well as the current clinical evidence in support of the continued, targeted use of clindamycin in dermatology.

Inflammation and the Gram-positive anaerobic bacterium Cutibacterium acnes, which is implicated in acne pathogenesis and pilosebaceous unit inflammation, are the main targets of antibiotic-based therapy against acne vulgaris (acne). The most widely used antibiotics in acne therapy are tetracyclines, macrolides, and lincosamides. Unfortunately, C. acnes bacteria over the past several decades have demonstrated increased resistance to these antibiotics, particularly to clindamycin. The precise knowledge of how antibiotics interact with their clinical target is needed to overcome this problem. Toward this goal, we determined the structure of clindamycin in complex with the ribosome of Cutibacterium acnes at 2.53 Å resolution using cryogenic electron microscopy. The galactose sugar moiety of clindamycin interacts with nucleotides of the 23S rRNA directly or through a conserved network of water-mediated interactions. Its propyl pyrrolidinyl group interacts with the 23S rRNA through van der Waals forces. Clindamycin binding to the Cutibacterium acnes ribosome interferes with both: proper orientation of the aminoacyl group of the A-site bound tRNA that is needed for peptide bond formation and with the extension of the nascent peptide. Our data are important for advancing understanding of antibiotic resistance and development of narrow- spectrum antibacterial drugs, which is an urgent need for contemporary antibiotic stewardship.

Clindamycin is a lincosamide antibiotic that has been used as a topical, oral, or injectable formulation for over five decades. It exhibits a narrow spectrum of microbiologic activity, primarily against gram-positive and anaerobic bacteria. In dermatology, clindamycin has been used primarily as a topical agent, usually for the treatment of acne vulgaris. Despite questions surrounding antibiotic resistance and/or its relative contribution to antibiotic treatment efficacy, a large body of data support the therapeutic value of topical clindamycin for acne vulgaris. As a systemic agent, clindamycin is used orally to treat a variety of cutaneous bacterial infections, and sometimes for acne vulgaris, with oral treatment for the latter less common in more recent years. The modes of action of clindamycin are supported by data showing both its anti-inflammatory and antibiotic mechanisms, which are discussed here along with pharmacokinetic profiles and structure-activity relationships. The diverse applications of clindamycin for multiple disease states, its efficacy, and safety considerations are also reviewed here, including for both topical and systemic formulations. Emphasis is placed on uses in dermatology, but other information on clindamycin relevant to clinicians is also discussed.

The human cytoskeleton consists of three major classes of filaments: microfilaments, microtubules and intermediate filaments. Here, we summarize recent progress in deciphering the structure and function of intermediate filaments and their implications for human disease.

Acne vulgaris is a chronic disfiguring skin disease affecting ∼1 billion people worldwide, often having persistent negative effects on physical and mental health. The Gram-positive anaerobe, Cutibacterium acnes is implicated in acne pathogenesis and is, therefore, a main target for antibiotic-based acne therapy. We determined a 2.8-Å resolution structure of the 70S ribosome of Cutibacterium acnes by cryogenic electron microscopy and discovered that sarecycline, a narrow-spectrum antibiotic against Cutibacterium acnes, may inhibit two active sites of this bacterium's ribosome in contrast to the one site detected previously on the model ribosome of Thermus thermophilus. Apart from the canonical binding site at the mRNA decoding center, the second binding site for sarecycline exists at the nascent peptide exit tunnel, reminiscent of the macrolides class of antibiotics. The structure also revealed Cutibacterium acnes-specific features of the ribosomal RNA and proteins. Unlike the ribosome of the Gram-negative bacterium Escherichia coli, Cutibacterium acnes ribosome has two additional proteins, bS22 and bL37, which are also present in the ribosomes of Mycobacterium smegmatis and Mycobacterium tuberculosis. We show that bS22 and bL37 have antimicrobial properties and may be involved in maintaining the healthy homeostasis of the human skin microbiome.

Supplementary Figure S1. Representative hematoxylin and eosin stained sections from sequenced LGSC; Supplementary Figure S2. Age distribution analysis of patients from the Australian Ovarian Cancer Study. Includes patients with advanced stage, serous epithelial ovarian cancer (n = 684); Supplementary Figure S3. RAS pathway mutations in LGSC; Supplementary Figure S4. Verification of EIF1AX mutations; Supplementary Figure S5. Characterization of the AOCS2 cell line; Supplementary Figure S6. Functional effect of EIF1AX mutations and gene suppression in a LGSC cell line; Supplementary Figure S7. (a) EIF1AX and NRAS function in the mTOR and RAS/ERK signaling pathways to regulate protein translation, cell proliferation and cell survival

Supplemental Material - Group Authorship from EIF1AX and NRAS Mutations Co-occur and Cooperate in Low-Grade Serous Ovarian Carcinomas

Antibiotic resistance is a global problem. Acne vulgaris is a chronic disfiguring skin disease affecting ∼1 billion people worldwide, often having persistent negative effects on physical and mental health. Prolonged treatment of acne with broad-spectrum antibiotics results in antibiotic resistance at concerning rates in the Gram-positive anaerobe Cutibacterium acnes, the skin commensal implicated in acne pathogenesis. We determined a 2.8-Å resolution structure of the 70S ribosome of Cutibacterium acnes by cryogenic electron microscopy and discovered that sarecycline, a narrow-spectrum antibiotic against Cutibacterium acnes, may inhibit two active sites of this bacterium's ribosome in contrast to the one site detected previously on the model ribosome of Thermus thermophilus. Apart from the canonical binding site at the mRNA decoding center, the second binding site for sarecycline exists at the nascent peptide exit tunnel, reminiscent of the macrolides class of antibiotics. The structure also revealed Cutibacterium acnes-specific features of the ribosomal RNA and proteins. Six Cutibacterium acnes ribosomal proteins bound Zn2+, providing molecular rationale for zinc supplementation in acne therapy. Unlike the ribosome of the Gram-negative bacterium Escherichia coli, Cutibacterium acnes ribosome has two additional proteins, which are also present in the ribosomes of Mycobacterium smegmatis and Mycobacterium tuberculosis. We show that these proteins have antimicrobial properties and may be involved in maintaining the healthy homeostasis of the human skin microbiome.