THE SERUM ALBUMIN-BINDING DOMAIN OF STREPTOCOCCAL PROTEIN-G IS A 3-HELICAL BUNDLE - A HETERONUCLEAR NMR-STUDY

Streptococcal protein G (SPG) is a cell surface receptor protein with a multiple domain structure containing tandem repeats of serum albumin -binding domains (ABD) and immuno-globulin-binding domains (IgBD), In this paper, me have analysed the fold of ABD, Far-UV circular dichrois m analysis of ABD indicates high helical content (56%), Based on an an alysis of nuclear magnetic resonance C-13 secondary chemical shifts, s equential and short-range NOEs, and a few key nuclear Overhauser effec ts, we conclude that the ABD is a three-helix bundle, The structure of the ABD is, thus, quite different from the IgBD of protein G [Gronenb orn, A.M. et al, (1991) Science 253, 657-661]. This strongly suggests that the ABD and the IgBD of SPG have evolved independently from each other, However, the fold of ABD is similar to that of the IgBD of stap hylococcal protein A, possibly indicating a common evolutionary ancest or, despite the lack of sequence homology.