Three new members of the serine-aspartate repeat protein multigene family of Staphylococcus aureus

Abstract

Three new genes encoding the serine-aspartate (SD) repeat-containing proteins SdrC, SdrD and SdrE were found in Staphy/ococcus aureus strain Newman. The SD repeats had earlier been found in the S. aureus fibrinogenbinding clumping factors ClfA and ClfB. The clfA and clfB genes encode highmolecular-mass f ibrinogen-binding proteins that are anchored to the cell surface of 5. aureus. The sdr genes now reported are closely linked and tandemly arrayed. The putative Sdr proteins have both organizational and sequence similarity to ClfA and ClfB. At the N-terminus, putative secretory signal sequences precede approximately 500 residue A regions. The A regions of the Sdr and Clf proteins exhibit only 20-30% residue identity when aligned with any other member of the family. The only conserved sequence is the consensus motif TYTFTDYVD. The Sdr proteins differ from ClfA and ClfB by having two to five additional 110-1 13 residue repeated sequences (B-motifs) located between region A and the R-region. Each B-motif contains a consensus Ca2+-binding EF-hand loop normally found in eukaryotic proteins. The structural integrity of recombinant SdrD(Bl-B5) protein comprising the five B-repeats of SdrD was shown by bisANS fluorescence analysis to be Ca2+-dependent, suggesting that the EF-hands are functional. When Ca2+ was removed the structure collapsed to an unfolded conformation. The original structure was restored by addition of Ca2? The C-terminal R-domains of the Sdr proteins contain 132-170 SD residues. These are followed by conserved wallanchoring regions characteristic of many surface proteins of Gram-positive bacteria. The sdr locus was present in all 31 5. aureus strains from human and bovine sources tested by Southern hybridization, although in a few strains it contained two rather than three genes.

A family of putative MSCRAMMs from Enterococcus faecalis

“…The MSCRAMM extension then acts as a latch, inserts into a cleft and complements a b-sheet of a neighbouring Ig-folded subdomain at the N terminus. The latching cleft contains a sequence motif TYTFTDYVD that is found in a similar position in all S. aureus MSCRAMMs identified so far (Josefsson et al, 1998;Ponnuraj et al, 2003). It is plausible that this binding mechanism is also used by other MSCRAMMs.…”

“…Pairwise amino acid identities in this region range from 21 to 30 % between any of the four proteins ClfA, ClfB, SdrG and EF1269. A conserved TYTFTDYVD-like motif is found in one of the two Ig-repeats (N1 in CNA, N2 in others) that form the ligand-binding region in staphylococcal MSCRAMMs (Josefsson et al, 1998;Ponnuraj et al, 2003). In the 'dock, lock and latch' ligand-binding model, this motif forms a cleft that accommodates the C-terminal latch extension of the neighbouring Ig-folded subdomain (Ponnuraj et al, 2003).…”

Characterization of novel LPXTG-containing proteins of Staphylococcus aureus identified from genome sequences

“…This explains the observation that PCR of sasG from genomic DNA isolated from a bacterial population generated a number of different sized fragments varying by the length of one repeat. The SdrD protein also contains a B repeat region which varies in the number of repeats between different strains (Josefsson et al, 1998a). PCR amplification of the sdrD gene from strain 8325-4, which bears five B repeat domains, yielded only a single PCR product.…”

“…This protein has a similar domain organization to proteins of the Sdr family (Josefsson et al, 1998a). It contains a large N-terminal A region which we propose to be composed of three separately folded subdomains, N1 (residues 91-244), N2 (residues 245-476) and N3 (residues 477-575).…”

“…The ClfA and ClfB A regions are composed of independently folded subdomains consisting primarily of b-sheets and coils with a small amount of a-helix (Perkins et al, 2001;Deivanayagam et al, 2002). Repeat regions occur as dipeptides in SD repeats of Sdr proteins (Josefsson et al, 1998a) that act as a stalk to project the N-terminal A region away from the bacterial cell surface (Hartford et al, 1997) or larger tandem repeated domains which vary in size and identity between proteins. The B repeats of Sdr proteins bind Ca 2+ and form rigid rod-like structures (Josefsson et al, 1998b) while the D repeats of the FnbpA and FnbpB proteins are flexible and bind fibronectin (McGavin et al, 1993;House-Pompeo et al, 1996).…”