A different path: Revealing the function of staphylococcal proteins in biofilm formation

Abstract

a b s t r a c tStaphylococcus aureus and Staphylococcus epidermidis cause dangerous and difficult to treat medical device-related infections through their ability to form biofilms. Extracellular poly-N-acetylglucosamine (PNAG) facilitates biofilm formation and is a vaccination target, yet details of its biosynthesis by the icaADBC gene products is limited. IcaC is the proposed transporter for PNAG export, however a comparison of the Ica proteins to homologous exo-polysaccharide synthases suggests that the common IcaAD protein components both synthesise and transport the PNAG. The limited distribution of icaC to the Staphylococcaceae and its membership of a family of membrane-bound acyltransferases, leads us to suggest that IcaC is responsible for the known O-succinylation of PNAG that occurs in staphylococci, identifying a potentially new therapeutic target specific for these bacteria.

The antifungal caspofungin increases fluoroquinolone activity against Staphylococcus aureus biofilms by inhibiting N-acetylglucosamine transferase

“…The gene products of the icaADBC locus include IcaA (transmembrane N -acetyl-glucosamine transferase synthesizing short PNAG polymers13), IcaD (protein increasing the biosynthetic efficiency of IcaA and playing a predominant role in the synthesis of oligomers longer than 20 residues13), IcaB (extracellular N -deacetylase enabling PNAG fixation at the bacterial cell surface and biofilm formation114), and IcaC (putative transmembrane protein initially considered as involved in the polymerization of short chain polymers13 but more recently, being recognized as a O -succinyltransferase catalyzing the O -modification of PNAG during biosynthesis15). Expression of icaA and subsequent PNAG production have been associated with the capacity of S. aureus to produce biofilm in vitro , including for clinical isolates collected from device-related infections161718.…”

Structural Basis for the De-N-acetylation of Poly-β-1,6-N-acetyl-d-glucosamine in Gram-positive Bacteria

“…IcaC is an integral membrane protein that was originally predicted to be responsible for exporting mature long-chain PNAG (21). However, the proposed function of IcaC has recently been revisited (23). Bioinformatics analysis predicts that IcaC contains 10 transmembrane helices and is a member of a large acetyltransferase family, suggesting it plays a role in the O-modification of PNAG during biosynthesis (23).…”

“…However, the proposed function of IcaC has recently been revisited (23). Bioinformatics analysis predicts that IcaC contains 10 transmembrane helices and is a member of a large acetyltransferase family, suggesting it plays a role in the O-modification of PNAG during biosynthesis (23). The presence of succinate groups on PNAG isolated from S. epidermidis (24) and S. aureus (25) supports the role of IcaC as an O-succinyltransferase.…”

Two repetitive, biofilm-forming proteins from Staphylococci: from disorder to extension

“…NMR spectroscopy of two 128-amino-constructs G5-E (a B-repeat) and E-G5 revealed that E is only folded when it neighbours a folded C-terminal G5; Xray crystallography revealed that, in the EG5 construct, both E and G5 form unusual, flat β-sheet structures (Figure 2b) [37]. As suggested for other highly repetitive bacterial surface proteins such as the Group B streptococcal protein Rib [38], the varying number of tandem repeats in SasG and Aap (3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17) [16,34], is probably a result of recombination facilitated by the high DNA sequence identity. However, although the DNA sequence identity might be advantageous, for example, for immune evasion [39], if each 128 amino acid repeat folded into a single domain, this would appear contrary to the observations made for proteins containing strings of Ig and Fn3 domains, where adjacent domains usually have sequence identity of less than 40 % [40], proposed to be necessary to reduce misfolding [41].…”

“…The next phase of biofilm formation is the accumulation/maturation stage in which cell-cell interactions dominate. The earliest studies implicated partially deacetylated polymeric N-acetylglucosamine (PNAG) or poly-saccharide intercellular adhesin (PIA), synthesized and modified by the ica-encoded proteins (IcaADBC) [4,5], in mediating staphylococcal biofilm formation. However, more recently, bacterial surface proteins involved in cell-cell interactions have also been identified [6].…”