Biogenesis of the Gram-positive bacterial cell envelope

Abstract

The Gram-positive cell envelope serves as a molecular platform for surface display of capsular polysaccharides, wall teichoic acids (WTAs), lipoteichoic acids (LTAs), lipoproteins, surface proteins and pili. WTAs, LTAs, and sortase-assembled pili are a few features that make the Gram-positive cell envelope distinct from the Gram-negative counterpart. Interestingly, a set of LytR-CpsA-Psr family proteins, found in all Gram-positives but limited to a minority of Gram-negative organisms, plays divergent functions, while decorating the cell envelope with glycans. Furthermore, a phylum of Gram-positive bacteria, the actinobacteria, appear to employ oxidative protein folding as the major folding mechanism, typically occurring in an oxidizing environment of the Gram-negative periplasm. These distinctive features will be highlighted, along with recent findings in the cell envelope biogenesis.

Sortase Transpeptidases: Structural Biology and Catalytic Mechanism

“…Gram-positive bacteria use sortase cysteine transpeptidase enzymes to covalently attach proteins to their cell wall, and to assemble pili. Sortases in pathogenic bacteria are frequently important virulence factors, as many of the proteins that they display have key roles in the infection process, such as promoting bacterial adhesion, nutrient acquisition, and the evasion and suppression of the immune response (Cascioferro, Totsika, & Schillaci, 2014; Schneewind & Missiakas, 2012, 2014; Siegel, Liu, & Ton-That, 2016; Spirig, Weiner, & Clubb, 2011). As a result, a significant amount of effort has been put forth to elucidate the mechanism of sortase-mediated catalysis and to discover small-molecule sortase inhibitors that could function as potent antiinfective agents (Bradshaw et al, 2015; Cascioferro et al, 2014; Clancy, Melvin, & McCafferty, 2010; Maresso & Schneewind, 2008; Suree, Jung, & Clubb, 2007).…”

“…In contrast to attaching proteins to the cell wall, a second type of sortase, frequently called “pilin polymerases,” construct bacterial pili by polymerizing pilin protein subunits (Fig. 2B) (Hendrickx, Budzik, Oh, & Schneewind, 2011; Kline, Dodson, Caparon, & Hultgren, 2010; Mandlik, Swierczynski, Das, & Ton-That, 2008; Siegel et al, 2016; Spirig et al, 2011; Ton-That & Schneewind, 2003). These pilin-assembling enzymes employ a similar transpeptidation reaction as SaSrtA, but instead of using lipid II as a nucleophile to attach proteins to the cell wall, a lysine amino group located within a protein pilin subunit is used as a secondary substrate to attack the sortase–protein thioacyl intermediate (Fig.…”

“…A number of excellent reviews have been written that describe the overall function of sortases in bacteria, their development as biochemical reagents, and efforts to discover therapeutically useful sortase inhibitors (Antos et al, 2016; Bradshaw et al, 2015; Cascioferro et al, 2014; Clancy et al, 2010; Maresso & Schneewind, 2008; Popp & Ploegh, 2011; Ritzefeld, 2014; Schmidt et al, 2017; Schmohl & Schwarzer, 2014; Schneewind & Missiakas, 2012, 2014; Siegel et al, 2016; Spirig et al, 2011; Suree et al, 2007; Voloshchuk et al, 2016). In this chapter, we review what is known about their atomic structures and the molecular basis of substrate recognition and catalysis.…”

Molecular Strategy for Blocking Isopeptide Bond Formation in Nascent Pilin Proteins

“…The presence of isopeptide and disulfide bonds in the Gram-positive pili proteins impede that these proteins fold in the cytoplasm, as absence of the bond is required for translocation to the periplasm (28,29). Pili proteins fold, acquire internal covalent bonds, and polymerize in the periplasm before the formation and anchoring of the pilus to the cell wall (29).…”

“…The presence of isopeptide and disulfide bonds in the Gram-positive pili proteins impede that these proteins fold in the cytoplasm, as absence of the bond is required for translocation to the periplasm (28,29). Pili proteins fold, acquire internal covalent bonds, and polymerize in the periplasm before the formation and anchoring of the pilus to the cell wall (29). In our experiments, as we express the isopeptide blocker in the cytoplasm before the translation of the Spy0128, we are mimicking this physiological condition, where a nascent translocating Spy0128 interacts with the isopeptide blocker within the periplasmic space ( Figure 1).…”