Vigilin interacts with signal peptide peptidase

Abstract

BackgroundSignal peptide peptidase (SPP), a member of the presenilin-like intra-membrane cleaving aspartyl protease family, migrates on Blue Native (BN) gels as 100 kDa, 200 kDa and 450 kDa species. SPP has recently been implicated in other non-proteolytic functions such as retro-translocation of MHC Class I molecules and binding of misfolded proteins in the endoplasmic reticulum (ER). These high molecular weight SPP complexes might contain additional proteins that regulate the proteolytic activity of SPP or support its non-catalytic functions.ResultsIn this study, an unbiased iTRAQ-labeling mass spectrometry approach was used to identify SPP-interacting proteins. We found that vigilin, a ubiquitous multi-KH domain containing cytoplasmic protein involved in RNA binding and protein translation control, selectively enriched with SPP. Vigilin interacted with SPP and both proteins co-localized in restricted intracellular domains near the ER, biochemically co-fractionated and were part of the same 450 kDa complex on BN gels. However, vigilin does not alter the protease activity of SPP, suggesting that the SPP-vigilin interaction might be involved in the non-proteolytic functions of SPP.ConclusionsWe have identified and validated vigilin as a novel interacting partner of SPP that could play an important role in the non-proteolytic functions of SPP. This data adds further weight to the idea that intramembrane-cleaving aspartyl proteases, such as presenilin and SPPs, could have other functions besides the proteolysis of short membrane stubs.

Mechanism, specificity, and physiology of signal peptide peptidase (SPP) and SPP-like proteases

“…These complexes with a molecular weight two to three times larger than that of the homotetrameric complex seem to differ in regard to substrate binding and binding of misfolded/unfolded proteins [57]. Recently, in a proteomic analysis of SPP binding partners, vigilin, a cytoplasmic protein involved in RNA binding and protein translation control, was found to interact with SPP in a high molecular weight complex, yet it did not alter or affect proteolytic activity of SPP [84]. This may indicate that SPP (and possibly SPPLs) forms high molecular weight complexes with additional binding partners that, though they do not to affect proteolytic activity, contribute to possible non-proteolytic functions of SPP/SPPLs.…”

Structural and Chemical Biology of Presenilin Complexes

“…Presenilin PS1 (and PS2) are the catalytic subunits of the heterotetrameric presenilin 1 (or presenilin 2) complexes (Wolfe et al 1999b;Li et al 2000a;Chen et al 2006;Ahn et al 2010) and are the founding members of the GXGD family of intramembranous aspartyl proteases. Other members of this protease family include signal peptide peptidases (SPP) and a variety of archaeal homologs (Weihofen et al 2002;Martoglio and Golde 2003;Friedmann et al 2004;Fluhrer et al 2009;Lu et al 2012a). These proteins will not be discussed in detail here except to note that they are monomeric or dimeric, and they have an opposite topology to the membrane relative to the presenilin proteins.…”

Structural biology of presenilin 1 complexes

“…PS1 (and PS2) are the catalytic subunits of the heterotetrameric presenilin 1 (or presenilin 2) complexes [ 29 , 31 ] and are the archetypal members of the GXGD family of intramembranous aspartyl proteases, which also includes signal peptide peptidases (SPP) and a variety of archaeal homologues [ 38 – 42 ].…”