The development and spread of antibiotic resistance in bacteria is a universal threat to both humans and animals that is generally not preventable, but can nevertheless be controlled and must be tackled in the most effective ways possible. To explore how the problem of antibiotic resistance might best be addressed, a group of thirty scientists from academia and industry gathered at the Banbury Conference Centre in Cold Spring Harbor, New York, May 16-18, 2011. From these discussions emerged a priority list of steps that need to be taken to resolve this global crisis.

A comprehensive sequence alignment of 64 members of the family of matrix metalloproteinases (MMPs) for the entire sequences, and subsequently the catalytic and the hemopexin-like domains, have been performed. The 64 MMPs were selected from plants, invertebrates, and vertebrates. The analyses disclosed that as many as 23 distinct subfamilies of these proteins are known to exist. Information from the sequence alignments was correlated with structures, both crystallographic as well as computational, of the catalytic domains for the 23 representative members of the MMP family. A survey of the metal binding sites and two loops containing variable sequences of amino acids, which are important for substrate interactions, are discussed. The collective data support the proposal that the assembly of the domains into multidomain enzymes was likely to be an early evolutionary event. This was followed by diversification, perhaps in parallel among the MMPs, in a subsequent evolutionary time scale. Analysis indicates that a retrograde structure simplification may have accounted for the evolution of MMPs with simple domain constituents, such as matrilysin, from the larger and more elaborate enzymes.

Aminoglycoside antibiotics have had a major impact on our ability to treat bacterial infections for the past half century. Whereas the interest in these versatile antibiotics continues to be high, their clinical utility has been compromised by widespread instances of resistance. The multitude of mechanisms of resistance is disconcerting but also illuminates how nature can manifest resistance when bacteria are confronted by antibiotics. This article reviews the most recent knowledge about the mechanisms of aminoglycoside action and the mechanisms of resistance to these antibiotics

Contents 1. Introduction 395 2. Penicillin-Binding Proteins 398 2.1. Enzymes of Cell Wall Biosynthesis 398 2.2. β-Lactam-Sensing Proteins 402 3. β-Lactamases 404 3.1. Overview and Classification 404 3.2. Class A β-Lactamases 406 3.3. Class C β-Lactamases 411 3.4. Class D β-Lactamases 412 3.5. Class B Metallo-β-lactamases 413 4. Other Resistance Mechanisms 416 4.1. Porin Deletion 416 4.2. Transporter Expression 417 5. Envoi 417 6. Acknowledgments 419 7. Abbreviations 419 8. Note Added in Proof 419 9. References 419 Scheme 1

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The 3D structure of the bacterial peptidoglycan, the major constituent of the cell wall, is one of the most important, yet still unsolved, structural problems in biochemistry. The peptidoglycan comprises alternating N-acetylglucosamine (NAG) and N-acetylmuramic disaccharide (NAM) saccharides, the latter of which has a peptide stem. Adjacent peptide stems are cross-linked by the transpeptidase enzymes of cell wall biosynthesis to provide the cell wall polymer with the structural integrity required by the bacterium. The cell wall and its biosynthetic enzymes are targets of antibiotics. The 3D structure of the cell wall has been elusive because of its complexity and the lack of pure samples. Herein we report the 3D solution structure as determined by NMR of the 2-kDa NAG-NAM(pentapeptide)-NAG-NAM(pentapeptide) synthetic fragment of the cell wall. The glycan backbone of this peptidoglycan forms a right-handed helix with a periodicity of three for the NAG-NAM repeat (per turn of the helix). The first two amino acids of the pentapeptide adopt a limited number of conformations. Based on this structure a model for the bacterial cell wall is proposed. This pentapeptide stem participates in an interglycan cross-linking reaction, thus creating the cell wall polymer. In contrast to the two other ␤-1,4-linked glycan biopolymers, cellulose (repeating glucose) (1-4) and chitin (repeating NAG) (5-7) for which the 3D structure is solved, the structure of the bacterial cell wall has remained elusive because of its complexity and the lack of pure and discrete segments for structural study (8-18). Herein we describe the 3D structure, determined in aqueous solution by NMR, of a 2-kDa synthetic NAG-NAM(pentapeptide)-NAG-NAM(pentapeptide) tetrasaccharide cell wall segment. The defining aspect of this structure is an ordered, right-handed helical saccharide conformation corresponding to three NAG-NAM pairs per turn of the helix. The structure of this peptidoglycan segment is the basis for a proposal for the structure of the bacterial cell wall polymer.Results and Discussion 3D Structure of the Peptidoglycan. Because of the critical significance of the cell wall to bacterial survival, and the exploitation of the cell wall biosynthetic enzymes for the chemotherapeutic intervention of infections, many experimental and theoretical studies have addressed the cell wall structure. Despite diffraction studies carried out Ͼ30 years ago on cell wall extracted from bacteria, which strongly suggested that the peptidoglycan polymer possessed regular order (11), the 3D structure of the cell wall is not known. An excellent account of the historical development of the hypotheses for the cell wall structure is given by Dmitriev, Toukach, and Ehlers in their recent review (18). The major reason for the lack of progress is the absence of a pure fragment of the cell wall, having both the peptide and disaccharide components of the peptidoglycan, for structural investigation. To address this limitation we completed the 37-step synthesis of such a segment (1...

. We determined that MMP-9 degrades the extracellular matrix protein laminin and that this degradation induces neuronal apoptosis in a transient focal cerebral ischemia model in mice. We also determined that the highly specific thiirane gelatinase inhibitor SB-3CT blocks MMP-9 activity, including MMP-9-mediated laminin cleavage, thus rescuing neurons from apoptosis. We conclude that MMP-9 is a highly promising drug target and that SB-3CT derivatives have significant therapeutic potential in stroke patients.

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