HSP47: Protein Type

Hsp47 is an ER-resident unique molecular chaperone crucially involved in the correct folding of procollagen ², ³. Hsp47 was characterized as being a basic protein with an isoelectric point of 9.0 ¹⁵. Hsp47 is a clade H member of the SERPIN superfamily of proteinase inhibitors and alternatively termed Serpin H1, but devoid of all inhibitory function. Hsp47 bears an N-terminal signal sequence, two N-glycosylation sites as well as a C-terminal ER-retention signal, RDEL ^{28, 29}. All serpins share a common secondary structure consisting of three β-sheets and at least seven α-helices ²⁴.  Similar to many other chaperones, Hsp47 is a phosphoprotein ³⁰ whose expression and function can be further modulated by co- and post-translational modifications such as N-glycosylation, succinylation, and acetylation ^31-33. To what extend phosphorylation especially affects the molecular or biological functions of the chaperone is still unclear. Free Hsp47 exists as a monomer in cells. Binding to procollagen is facilitated by two Hsp47 molecules that associate head-to-head to one procollagen trimer, thereby forming the oligomeric chaperone-procollagen complex ²⁴.