HSP47: Molecular Weight

Hsp47, also known as Serpin H1, is a procollagen-specific molecular chaperone residing in the endoplasmic reticulum. Hsp47 belongs to clade H of the SERPIN superfamily of proteinase inhibitors. The SERPIN family exhibits the most common proteinase inhibitors comprising polypeptides whose molecular weights range from 21 to 55 kDa and that are encoded by a multigene family encompassing 36 putatively functional protein-coding genes and 5 pseudogenes in humans ³⁴. Functional genes encoding serpins map to several human chromosomes as given in Table 2. Hsp47/Serpin H1 is encoded by a single-copy nuclear gene, SERPINH1 clustered on chromosome 11q13.5 and translated in the cytosol. One pseudogene has been found as being associated with this gene, termed SERPINH1P and located to chromosome 9p13.3. The coding sequence of the expressed protein consists of 418 amino acid residues yielding a molecular mass of 46.4 kDa. Cleavage of the N-terminal signal peptide (aa 1 – 18) generates the mature Hsp47 protein with 400 amino acids and a molecular mass of 44.5 kDa which is further processed by co- and post-translational modifications, respectively.  Beside its monomeric form, recombinant human and mouse Hsp47 have recently been found to form oligomers 130 kDa in size and indicative for the formation of homotrimers ²³. This observation is in line with previous findings on mature recombinant mouse Hsp47 made by Dafforn and colleagues. The group identified the existence of a hyperstable, biologically active trimeric variant of Hsp47 together with an – also biologically active – structurally mesostable monomer ³⁵.