MSP (Macrophage stimulating protein 1; also hepatocyte growth factor-like protein) is an 80-95 kDa member of the peptidase S1 family of proteins. Although it is expressed principally by hepatocytes, it can also be induced in cells such as renal tubular epithelium. MSP has multiple targets, and as such, has multiple effects. It stimulates macrophage motility and phagocytosis, promotes keratinocyte and renal tubular cell proliferation, and depresses myeloid progenitor cell replication. Mouse proMSP is 698 amino acids (aa) in length. It contains one PAN (carbohydrate-binding) site (aa 19-105), four consecutive kringle domains (110-457) and an inactive peptidase S1 region (aa 489-714). An intrachain disulfide bond exists between Cys477 and Cys593 that becomes an interchain bond following protease cleavage between Arg488 and Val489. This creates a mature heterodimer containing a 45-57 kDa alpha -chain, and a 30-35 kDa beta -chain. Mouse proMSP shares 80% and 93% aa identity with human and rat proMSP, respectively.