Folding mechanism of a multiple independently-folding domain protein: double B domain of protein A.

Journal Article (Journal Article)

The antibody binding properties of staphylococcal protein A (SpA) can be attributed to the presence of five highly homologous domains (E, D, A, B, and C). Although the folding of the B domain of protein A (BdpA) is well-characterized, the folding behavior of this domain in the context of full-length SpA in the cell remains unexplored. The sequence of the B domain is 89 and 91% identical to those of domains A and C, respectively. We have fused B domain sequences (BBdpA) as a close approximation of the A-B or B-C portion of SpA. Circular dichroism and fluorescence-detected denaturation curves of BBdpA are experimentally indistinguishable from those of BdpA. The rate constants for folding and unfolding from NMR line shape analysis for the single- and double-domain proteins are the same within experimental uncertainties (+/-20%). These results support the designation of SpA as a multiple independently-folding domain (MIFD) protein. We develop a mathematical model that describes the folding thermodynamics and kinetics of MIFD proteins. The model depicts MIFD protein folding and unfolding as a parallel network and explicitly calculates the flux through all parallel pathways. These fluxes are combined to give a complete description of the global thermodynamics and kinetics of the folding and unfolding of MIFD proteins. The global rates for complete folding and unfolding of a MIFD protein and those of the individual domains depend on the stability of the protein. We show that the global unfolding rate of a MIFD protein may be many orders of magnitude slower than that of the constituent domains.

Full Text

Duke Authors

Cited Authors

  • Arora, P; Hammes, GG; Oas, TG

Published Date

  • October 10, 2006

Published In

Volume / Issue

  • 45 / 40

Start / End Page

  • 12312 - 12324

PubMed ID

  • 17014084

International Standard Serial Number (ISSN)

  • 0006-2960

Digital Object Identifier (DOI)

  • 10.1021/bi060923s


  • eng

Conference Location

  • United States