Kinetic stabilisation of a modular protein by domain interactions

Abstract
Protein S, a two‐domain spore coat protein from Myxococcus xanthus, is structurally related to eye‐lens βγ‐crystallins. No natural monomeric one‐domain member of this protein superfamily is known. To determine the stability of the single domains and to explain the ubiquitous domain duplication, the isolated domains of protein S were constructed. The N‐domain is thermodynamically more stable than the C‐domain. In intact protein S, domain interactions lead to an apparent decrease in stability of the N‐terminal domain, whereas the C‐terminal domain is stabilised. In contrast, unfolding kinetics of both domains are decreased 100‐fold due to interactions in the complete molecule.