Using offset recombinant polymerase chain reaction to identify functional determinants in a common family of bacterial albumin binding domains

The 46 amino acid GA albumin binding module is a putative virulence factor that has been identified in 16 domains from four bacterial species. Aside from their possible effects on pathogenicity and host specificity, the natural genotypic and phenotypic variations that exist among members of this module offer unique opportunities for researchers to identify and explore functional determinants within the well-defined sequence space. We used a recently developed in vitro recombination technique, known as offset recombinant PCR, to shuffle seven homologues that encode a broad range of natural GA polymorphisms. Phage display and selection were applied to probe the recombinant library for members that showed simultaneous improvements to human and guinea pig serum albumin binding. Thermodynamic data for the most common phage-selected mutant suggest that domain-stabilizing mutations substantially improved GA binding for both species of albumin.