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The structure of ?-haemoglobin in complex with a haemoglobin-binding domain from Staphylococcus aureus reveals the elusive ?-haemoglobin dimerization interface.

ABSTRACT: Adult haemoglobin (Hb) is made up of two ? and two ? subunits. Mutations that reduce expression of the ?- or ?-globin genes lead to the conditions ?- or ?-thalassaemia, respectively. Whilst both conditions are characterized by anaemia of variable severity, other details of their pathophysiology are different, in part owing to the greater stability of the ? chains that is conferred through ? self-association. In contrast, ? subunits interact weakly, and in the absence of stabilizing quaternary interactions the ? chain (?) is prone to haem loss and denaturation. The molecular contacts that confer weak self-association of ? have not been determined previously. Here, the first structure of an ?2 homodimer is reported in complex with one domain of the Hb receptor from Staphylococcus aureus. The ?2 dimer interface has a highly unusual, approximately linear, arrangement of four His side chains within hydrogen-bonding distance of each other. Some interactions present in the ?1?1 dimer interface of native Hb are preserved in the ?2 dimer. However, a marked asymmetry is observed in the ?2 interface, suggesting that steric factors limit the number of stabilizing interactions that can form simultaneously across the interface.

SUBMITTER: Kumar KK

PROVIDER: S-EPMC4118798 | biostudies-literature | 2014 Aug

REPOSITORIES: biostudies-literature

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The structure of α-haemoglobin in complex with a haemoglobin-binding domain from Staphylococcus aureus reveals the elusive α-haemoglobin dimerization interface.

Kumar Kaavya Krishna KK Jacques David A DA Guss J Mitchell JM Gell David A DA

Acta crystallographica. Section F, Structural biology communications 20140723 Pt 8

Adult haemoglobin (Hb) is made up of two α and two β subunits. Mutations that reduce expression of the α- or β-globin genes lead to the conditions α- or β-thalassaemia, respectively. Whilst both conditions are characterized by anaemia of variable severity, other details of their pathophysiology are different, in part owing to the greater stability of the β chains that is conferred through β self-association. In contrast, α subunits interact weakly, and in the absence of stabilizing quaternary in ...[more]

PMID: 25084376

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Project description:BackgroundFibronectin-binding protein A (FnBPA) mediates adhesion of Staphylococcus aureus to fibronectin, fibrinogen and elastin. We previously reported that S. aureus strain P1 encodes an FnBPA protein where the fibrinogen/elastin-binding domain (A domain) is substantially divergent in amino acid sequence from the archetypal FnBPA of S. aureus NCTC8325, and that these variations created differences in antigenicity. In this study strains from multilocus sequence types (MLST) that spanned the genetic diversity of S.aureus were examined to determine the extent of FnBPA A domain variation within the S. aureus population and its effect on ligand binding and immuno-crossreactivity.ResultsSeven different isotype forms (I - VII) of the FnBPA A domain were identified which were between 66 to 76% identical in amino acid sequence in any pair-wise alignment. The fnbA allelic variants in strains of different multilocus sequence type were identified by DNA hybridization using probes specific for sequences encoding the highly divergent N3 sub-domain of different isotypes. Several isotypes were not restricted to specific clones or clonal complexes but were more widely distributed. It is highly likely that certain fnbA genes have been transferred horizontally. Residues lining the putative ligand-binding trench were conserved, which is consistent with the ability of each A domain isotype to bind immobilized fibrinogen and elastin by the dock-latch-lock mechanism. Variant amino acid residues were mapped on a three-dimensional model of the FnBPA A domain and were predicted to be surface-exposed. Polyclonal antibodies raised against the recombinant isotype I A domain bound that protein with a 4 - 7 fold higher apparent affinity compared to the A domains of isotypes II - VII, while some monoclonal antibodies generated against the isotype I A domain showed reduced or no binding to the other isotypes.ConclusionThe FnBPA A domain occurs in at least 7 different isotypes which differ antigenically and exhibit limited immuno-crossreactivity, yet retain their ligand-binding functions. Antigenic variation of the FnBPA A domain may aid S. aureus to evade the host's immune responses. These findings have implications for the development of vaccines or immunotherapeutics that target FnBPA.

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Dataset Information

The structure of ?-haemoglobin in complex with a haemoglobin-binding domain from Staphylococcus aureus reveals the elusive ?-haemoglobin dimerization interface.

Publications

The structure of α-haemoglobin in complex with a haemoglobin-binding domain from Staphylococcus aureus reveals the elusive α-haemoglobin dimerization interface.

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