Abstract
Poly(aspartic acid) (PAA) is a common water-soluble polycarboxylate used in a broad range of applications. PAA biodegradation and environmental assimilation were first identified in river water bacterial strains, Sphingomonas sp. KT-1 and Pedobacter sp. KP-2. Within Sphingomonas sp. KT-1, PahZ1(KT-1) cleaves β-amide linkages to oligo(aspartic acid) and then is degraded by PahZ2(KT-1). Recently, we reported the first structure for PahZ1(KT-1). Here, we report novel structures for PahZ2(KT-1) bound to either Gd(3+)/Sm(3+) or Zn(2+) cations in a dimeric state consistent with M28 metallopeptidase family members. PahZ2(KT-1) monomers include a dimerization domain and a catalytic domain with dual Zn(2+) cations. MD methods predict the putative substrate binding site to span across the dimerization and catalytic domains, where NaCl promotes the transition from an open conformation to a closed conformation that positions the substrate adjacent to catalytic zinc ions. Structural knowledge of PahZ1(KT-1) and PahZ2(KT-1) will allow for protein engineering endeavors to develop novel biodegradation reagents.