3-DIMENSIONAL SOLUTION STRUCTURE OF THE PLECKSTRIN HOMOLOGY DOMAIN FROM DYNAMIN

Background: The pleckstrin homology (PH) domain is a region of approxi mately 100 amino acids, defined by sequence similarity, that has been found in about 60 proteins, many of which are involved in signal trans duction downstream of cell surface receptors; the function of PH domai ns is unknown. The only clue to the function of PH domains is the circ umstantial evidence that they may link beta gamma subunits of G protei ns to second messenger systems. Knowledge of the three-dimensional str uctures of PH domains should help to elucidate the roles they play in the proteins that contain them. Results: Using homonuclear and heteron uclear magnetic resonance spectroscopy, we have determined the solutio n structure of the PH domain of the GTPase dynamin, one of a number of proteins that have PH domains and interact with GTP. The fold of the dynamin PH domain is composed of two antiparallel beta-sheets, which p ack face-to-face at an angle of approximately 60 degrees. The first be ta-sheet comprises four strands (residues 13-58) from the amino-termin al half of the protein sequence; the second beta-sheet contains three strands (residues 63-99). A single alpha-helix (residues 102-116) flan ks one edge of the interface between the two sheets, parallel in orien tation to the second sheet, in an alpha/beta roll motif similar to tha t of the B oligomer of verotoxin-l from Escherichia coli. Conclusions: The structure of the dynamin PH domain is very similar to the recentl y reported structures of the pleckstrin and spectrin PH domains. This shows that, despite the low level of sequence similarity between diffe rent PH domains, they do have a characteristic polypeptide fold. On th e basis of our structure, the suggestion that PH domains engage in coi led-coil interactions with G protein beta gamma subunits seems unlikel y and should be re-evaluated.