A novel variant of the immunoglobulin fold in surface adhesins of Staphylococcus aureus: crystal structure of the fibrinogen-binding MSCRAMM, clumping factor A

Abstract

We report here the crystal structure of the minimal ligand-binding segment of the Staphylococcus aureus MSCRAMM, clumping factor A. This ®brinogen-binding segment contains two similarly folded domains. The fold observed is a new variant of the immunoglobulin motif that we have called DE-variant or the DEv-IgG fold. This subgroup includes the ligand-binding domain of the collagen-binding S.aureus MSCRAMM CNA, and many other structures previously classi®ed as jelly rolls. Structure predictions suggest that the four ®brinogen-binding S.aureus MSCRAMMs identi®ed so far would also contain the same DEv-IgG fold. A systematic docking search using the C-terminal region of the ®brinogen g-chain as a probe suggested that a hydrophobic pocket formed between the two DEv-IgG domains of the clumping factor as the ligand-binding site. Mutagenic substitution of residues Tyr256, Pro336, Tyr338 and Lys389 in the clumping factor, which are proposed to contact the terminal residues 408 AGDV 411 of the g-chain, resulted in proteins with no or markedly reduced af®nity for ®brinogen.

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

“…Most LPXTG proteins of S. aureus contain a~500 residue A region, which has recently been proposed to be composed of three independently folded subdomains in the case of ClfA and ClfB (Perkins et al, 2001;Deivanayagam et al, 2002). N1 is extremely hydrophilic with an elongated secondary structure, whereas N2 and N3 are globular proteins bearing the ligand binding activity.…”

“…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). Residues 91-244 of SasA contain a high proportion of hydrophilic residues similar to domain N1 of ClfA and ClfB (28 % serine compared to 9 % serine in the rest of the A region; Perkins et al, 2001;Deivanayagam et al, 2002). This is probably responsible for the aberrant migration of recombinant proteins on SDS-PAGE gels.…”

“…Many share a common domain organization with a similar sized Nterminal A region (ca 500 residues) which contains ligand binding activity. 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.…”

Characterization of the fibrinogen-binding surface protein Fbl of Staphylococcus lugdunensis

“…Structural analysis of ClfA and the related fibrinogenbinding proteins SdrG and ClfB revealed that the ligandbinding A domain is composed of three subdomains called N1, N2 and N3 (Deivanayagam et al, 2002;Ponnuraj et al, 2003). The structure of smallest truncate of the ClfA A domain that retains the ability to bind fibrinogen (residues 220-559; sometimes called N2N3) has been solved.…”

“…The structure of smallest truncate of the ClfA A domain that retains the ability to bind fibrinogen (residues 220-559; sometimes called N2N3) has been solved. Each subdomain comprises nine b-strands that form a novel IgG-type fold (Deivanayagam et al, 2002). The fibrinogen c-chain peptide-binding site is located in a hydrophobic groove at the junction between N2 and N3.…”