Comparison of SH3 and SH2 domain dynamics when expressed alone or in an SH(3+2) construct: The role of protein dynamics in functional regulation

Protein dynamics play an important role in protein function and regulation of enzymatic activity. To determine how additional interactions with surrou nding structure affects local protein dynamics, we have used hydrogen excha nge and mass spectrometry to investigate the SH2 and SH3 domains of the pro tein tyrosine kinase Hck. Exchange rates of isolated Hck SH3 and SH2 domain s were compared with rates for the same domains when part of a larger SH(3 +/- 2) construct. Increased deuterium incorporation was observed for the SH 3 domain in the joint construct, particularly near the SH2 interface and th e short sequence that connects SH3 to SH2, implying greater flexibility of SH3 when it is part of SH(3 + 2). Slow cooperative unfolding of the SH3 dom ain occurred at the same rate in isolated SH3 as in the SH(3 + 2) construct , suggesting a functional significance for this unfolding. The SH2 domain d isplayed relatively smaller changes in flexibility when part of the SH(3 +/ - 2) construct. These results suggest that the domains influence each other . Further, our results imply a link between functional regulation and struc tural dynamics of SH3 and SH2 domains. (C) 1999 Academic Press.