Structure and kinetic characterization of human sperm-specific glyceraldehyde-3-phosphate dehydrogenase, GAPDS

Apirat Chaikuad , Naeem Shafqat , Ruby Al-Mokhtar , Gus Cameron , Anthony R Clarke , Leo Brady , Udo Oppermann , Jan Frayne , Wyatt W. Yue (1)

1 Structural Genomics Consortium

Human sperm-specific glyceraldehyde-3-phosphate dehydrogenase (hGAPDS) is a glycolytic enzyme essential for the survival of spermatozoa, and constitutes a potential target for non-hormonal contraception. However, enzyme characterization of GAPDS has been hampered by the difficulty in producing soluble recombinant protein. Here, we have over-expressed in E. coli a highly-soluble form of hGAPDS truncated at the N-terminus (hGAPDS∆N), and crystallized the homo-tetrameric enzyme in two ligand complexes. The hGAPDS∆N-NAD+-phosphate structure maps the two anion recognition sites within the catalytic pocket that correspond to the conserved Ps site and the newly recognised Pi site identified in other organisms. The hGAPDS∆N-NAD+-glycerol structure shows serendipitous binding of glycerol at the Ps and new Pi sites, demonstrating the propensity of these anion recognition sites to bind non-physiologically-relevant ligands. A comparison of kinetic profiles between hGAPDS∆N and its somatic equivalent reveals a moderate 3-fold increase in catalytic efficiency for hGAPDS∆N. This may be attributable to subtle amino acid substitutions peripheral to the active centre that influence the charge properties and protonation states of catalytic residues. Our data therefore elucidate structural and kinetic features of hGAPDS that might provide insightful information towards inhibitor development.

Mots clés: Life Sciences

Apirat Chaikuad, Naeem Shafqat, Ruby Al-Mokhtar, Gus Cameron, Anthony R Clarke, et al.. Structure and kinetic characterization of human sperm-specific glyceraldehyde-3-phosphate dehydrogenase, GAPDS. Biochemical Journal, 2011, 435 (2), pp.401-409. ⟨10.1042/BJ20101442⟩. ⟨hal-00581535⟩