Human progelatinase B consists of 668 amino acids with a calculated Mr of 76240 Da. Due to N- and O-linked glycosylation the Mr in SDS-PAGE is about 92 kDa. Within the protein sequence the following structural domains can be distinguished: An N-terminal propeptide, which confers latency to the proenzyme, a Ca2+ - and Zn2+ -ions binding catalytic domain containing an insertion of three repeats homologous to type II repeats in the gelatin-binding region of fibronectin, and a C-terminal hemopexin-like domain. Catalytic and hemopexin domains are connected by a proline-rich sequence with homology to sequences in collagens. The gelatin binding region and the hemopexin domain confer specific macromolecular substrate binding to gelatinase B. The hemopexin domain of the latent enzyme binds TIMP-1. Gelatinase B from neutrophil granulocytes displays three bands on SDS-PAGE (reducing condition) at 92, 29 and 25 kDa. The 92 kDa form represents the monomer, the 29 kDa protein band represents TIMP 1 and the 25 kDa protein which belongs to the lipocalin family and displays homology with the a2- macroglobulin related protein from rats. These proteins are capable of forming complexes, including the binary MMP9/ TIMP1 complex, which behaves like the ternary MMP9/ Lipocalin/ TIMP1 complex that it is an inhibitor for active MMPs and, after activation, a gelatinase with a reduced activity.

Secreted