The human complement regulator factor H binds pneumococcal surface protein PspC via short consensus repeats 13 to 15.
The innate ability of Streptococcus pneumoniae to resist complement activation and complement-mediated phagocytosis may be a direct consequence of the ability of the bacteria to bind components of the complement regulatory system. One such component, factor H (fH), is a crucial fluid-phase negative regulator of the alternative pathway of complement and is utilized by a number of pathogenic organisms to resist complement attack. The pneumococcal surface protein C (PspC [also known as CbpA] and SpsA) has been shown to bind fH, although the exact binding site within one or more of the 20 short consensus repeats (SCRs) of the molecule is not known. The purpose of the current study was to map specific SCRs on fH responsible for this binding. Initial experiments utilizing type 2 pneumococcal strain D39 and its isogenic PspC-negative derivative (D39/pspC mutant) showed that fH binding was PspC dependent. A purified recombinant protein derivative of PspC that lacked the proline-rich region (PspCDeltaPro) had a reduced binding efficiency for fH, thereby directly showing the importance of this region for the fH interaction. We have specifically shown by inhibition experiments that SCRs responsible for heparin and C3b binding of fH are not involved in binding PspC and the interaction between fH and PspC is largely hydrophobic, since no inhibition was observed in the presence of high concentrations of NaCl. Construction of SCR proteins encompassing the whole fH molecule showed that SCRs 8 to 15 (SCR 8-15) mediated binding to PspC. Further localization experiments revealed that SCR 13 and SCR 15 were required for full binding, although partial binding was retained when either SCR was removed.
Duthy
Thomas G
TG
Department of Microbiology and Infectious Diseases, Flinders Medical Centre, Bedford Park, South Australia 5042, Australia.
Ormsby
Rebecca J
RJ
Giannakis
Eleni
E
Ogunniyi
A David
AD
Stroeher
Uwe H
UH
Paton
James C
JC
Gordon
David L
DL
D001426:Bacterial Proteins / Q000378:metabolism*; D001483:Base Sequence; D001665:Binding Sites / Q000235:genetics; D003179:Complement C3b / Q000494:pharmacology; D017242:Complement Factor H / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D016384:Consensus Sequence; D004274:DNA, Recombinant / Q000235:genetics; D006493:Heparin / Q000494:pharmacology; D006801:Humans; D066298:In Vitro Techniques; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D020449:Repetitive Sequences, Amino Acid; D012965:Sodium Chloride / Q000494:pharmacology; D013296:Streptococcus pneumoniae / Q000378:metabolism
D001426:Bacterial Proteins; C493495:CFH protein, human; D004274:DNA, Recombinant; D011994:Recombinant Proteins; C110344:SpsA protein, Streptococcus pneumoniae; D012965:Sodium Chloride; D003179:Complement C3b; D017242:Complement Factor H; D006493:Heparin