BaP1 is a 22.7-kD P-I-type
zinc-dependent
metalloproteinase isolated from the
venom of the snake Bothrops asper, a medically relevant species in Central America. This
enzyme exerts multiple tissue-damaging activities, including
hemorrhage, myonecrosis, dermonecrosis, blistering, and
edema. BaP1 is a single chain of 202
amino acids that shows highest sequence identity with
metalloproteinases isolated from the
venoms of snakes of the subfamily Crotalinae. It has six Cys residues involved in three
disulfide bridges (Cys 117-Cys 197, Cys 159-Cys 181, Cys 157-Cys 164). It has the consensus sequence
H(142)E(143)XXH(146)XXGXXH(152), as well as the sequence C(164)I(165)M(166), which characterize the "metzincin" superfamily of
metalloproteinases. The active-site cleft separates a major subdomain (residues 1-152), comprising four alpha-helices and a five-stranded beta-sheet, from the minor subdomain, which is formed by a single alpha-helix and several loops. The catalytic
zinc ion is coordinated by the N(epsilon 2)
nitrogen atoms of His 142, His 146, and His 152, in addition to a
solvent water molecule, which in turn is bound to Glu 143. Several conserved residues contribute to the formation of the hydrophobic pocket, and Met 166 serves as a hydrophobic base for the active-site groups. Sequence and structural comparisons of hemorrhagic and nonhemorrhagic P-I
metalloproteinases from
snake venoms revealed differences in several regions. In particular, the loop comprising residues 153 to 176 has marked structural differences between
metalloproteinases with very different hemorrhagic activities. Because this region lies in close proximity to the active-site microenvironment, it may influence the interaction of these
enzymes with physiologically relevant substrates in the extracellular matrix.