Procollagen C-proteinase enhancer grasps the stalk of the C-propeptide trimer to boost collagen precursor maturation

Abstract

Tight regulation of collagen fibril deposition in the extracellular matrix is essential for normal tissue homeostasis and repair, defects in which are associated with several degenerative or fibrotic disorders. A key regulatory step in collagen fibril assembly is the C-terminal proteolytic processing of soluble procollagen precursors. This step, carried out mainly by bone morphogenetic protein-1/tolloid-like proteinases, is itself subject to regulation by procollagen C-proteinase enhancer proteins (PCPEs) which can dramatically increase bone morphogenetic protein-1/tolloid-like proteinase activity, in a substrate-specific manner. Although it is known that this enhancing activity requires binding of PCPE to the procollagen C-propeptide trimer, identification of the precise binding site has so far remained elusive. Here, use of small-angle X-ray scattering provides structural data on this protein complex indicating that PCPE binds to the stalk region of the procollagen C-propeptide trimer, where the three polypeptide chains associate together, at the junction with the base region. This is supported by site-directed mutagenesis, which identifies two highly conserved, surface-exposed lysine residues in this region of the trimer that are essential for binding, thus revealing structural parallels with the interactions of Complement C1r/C1s, Uegf, BMP-1 (CUB) domain-containing proteins in diverse biological systems such as complement activation, receptor signaling, and transport. Together with detailed kinetics and interaction analysis, these results provide insights into the mechanism of action of PCPEs and suggest clear strategies for the development of novel antifibrotic therapies.proteolysis | structural proteins | fibrosis R egulation of collagen deposition in the extracellular matrix is essential for normal tissue homeostasis and repair, defects in which are associated with numerous, often lethal, disorders, including chronic wounds and the many different forms of fibrosis (affecting heart, lung, liver, kidney, skin, etc.) (1, 2). At the protein level, a key regulatory step is the proteolytic conversion of soluble precursor molecules, procollagens, by removal of N-and C-propeptides (3), resulting in spontaneous assembly of collagen fibrils. Although collagen deposition in vivo is also controlled by numerous interactions with cell-surface and extracellular matrix proteins (4, 5), it is generally acknowledged that a key ratelimiting step is the proteolytic removal of the procollagen Cpropeptides. The principal proteinases involved here are zinc metalloproteinases, called bone morphogenetic protein-1 (BMP-1)/tolloid-like proteinases (collectively known as BTPs), which cleave the C-propeptides from the major fibrillar procollagens (types I, II, and III) (3,(6)(7)(8).Although BTPs cleave a number of extracellular substrates (including structural proproteins, proenzymes, and latent growth factors or their antagonists) (8, 9), their activity on fibrillar procollagens is specifically increased, several-fold, by procollag...

BMP-1/tolloid-like proteinases synchronize matrix assembly with growth factor activation to promote morphogenesis and tissue remodeling

“…(C) Diagram of the horseshoe shape of BMP-1 deduced by Berry et al [10]. (D) Interaction of the CUB1CUB2 region of PCPE-1 with the stalk region of the procollagen III C-propeptide trimer (CPIII) [57]. remove the N-terminal extensions of procollagens I-III (N-propeptides; see the review by Colige & Bekhouche in this special issue), BTPs are the main enzymes in charge of the rate-limiting step of fibril formation, that is the removal of the C-terminal propeptides.…”

“…Initially co-purified with BMP-1 from mouse fibroblasts [55], PCPE-1 is a 55 kDa ubiquitous glycoprotein devoid of catalytic activity but able to enhance C-propeptide removal from procollagens I-III up to 10 fold [55][56][57]. Of the three domains forming PCPE-1 ( Fig.…”

“…1A; CUB1-CUB2-NTR), only the contiguous CUB domain region is necessary and sufficient for its activity [58][59][60]; the NTR domain, which is homologous to TIMPs, is however able to interact with heparan sulfate proteoglycans (HSPGs), thus mediating PCPE-1 anchoring to the cell surface and allowing an even greater stimulation of BMP-1 activity [61,62]. Recent biochemical and structural studies [57,59,63] have dissected the mechanism of action of PCPE-1 and shown that it functions via direct and tight binding to the stalk region of the C-propeptide trimer, close to the cleavage site, with a 1:1 stoichiometry (Fig. 1D).…”

The NTR domain of procollagen C-proteinase enhancer-1 (PCPE-1) mediates PCPE-1 binding to syndecans-1, -2 and -4 as well as fibronectin

“…PCPE-1 consists of two N-terminal CUB domains that bind to the procollagen C-propeptide and are responsible for enhancing activity (Kessler and Adar, 1989;Takahara et al, 1994;Hulmes et al, 1997;Ricard-Blum et al, 2002;Vadon-Le Goff et al, 2011;Bourhis et al, 2013) and a C-terminal NTR (netrin-like) domain that binds to heparin and heparan sulfate (Moschcovich et al, 2001;Weiss et al, 2010). This latter interaction induces further enhancement of procollagen processing by BMP-1, an effect referred to as superstimulation (Beckhouche et al, 2010).…”

Synergistic effect of PCPE1 and sFRP2 on the processing of procollagens via BMP1

“…Moreover, the C-proteinase activity of BMP-1 was found to be promoted by some particular proteins, such as fibronectin, Procollagen C-Proteinase Enhancer 1 (PCOLCE1; PCPE1), and Secreted Frizzled-Related Protein 2 (sFRP2) [12][13][14]. It has been shown that PCPE1, a secreted 55-kDa extracellular glycoprotein, drives the enzymatic cleavage of type I procollagen via enhancing BMP1 activity in a substrate-specific manner [15][16][17][18]. PCPE1 has three major protein domains: two CUB domains and a C-terminal netrin-like (NTR) domain [19].…”