Novel functional domains in the muscle disease associated protein KY

Kyphoscoliosis Peptidase (KY) is a skeletal muscle Z-disk protein that has been implicated in several inherited myopathies. The mechanism underpinning KY’s function has remained elusive, but previous research suggests that KY could have protease activity over generic substrates. However, protease activity over endogenous substrates have not been proven. The highly conserved transglutaminase/protease (TGN/PROT) domain is the only distinguishable feature within KY. This domain includes conservation of the three catalytic residues which have been shown to be required for enzymatic activity in cysteine proteases. Here, biochemical assays have shown that this domain is not enzymatically active. In addition, electroporations of the ky/ky mouse muscle with a KY version lacking the TGN/PROT domain indicates that this domain is not required for Z-disk localisation but is required for the rescue of atrophic muscle fibres.

Here, in-silico analysis has shown that human KY (hKY) protein has gained a nuclear localisation signal (NLS) located upstream of the putative start site of the mouse and other vertebrate homologues. This NLS appears to be functional, as in contrast to the
mouse KY protein, hKY shows nuclear localisation in C2C12 myoblasts and COS-7 fibroblasts. Within electroporated adult mouse muscle hKY localises both to the Z-disk and the nucleus. The Z-disc/nuclear localization of hKY is highly reminiscent of IGFN1, a known protein partner of mouse KY. Co-transfections of hKY and IGFN1 in C2C12 myoblasts leads to strong accumulation of both protein in nuclear aggregates, while IGFN1 is not able to change localization of mouse KY to the nucleus. Thus, the mouse and human KY orthologues show different expression patterns. Further analysis shows that this NLS is conserved within primates and
therefore may have evolved to facilitate the distinct biomechanics of primate muscles compared to other placental mammals.