Structural Basis for the Acceleration of Procollagen Processing by Procollagen C-Proteinase Enhancer-1

Abstract

Procollagen C-proteinase enhancer-1 (PCPE-1) is a secreted protein that specifically accelerates proteolytic release of the C-propeptides from fibrillar procollagens, a crucial step in fibril assembly. As such, it is a potential therapeutic target to improve tissue repair and prevent fibrosis, a major cause of mortality worldwide. Here we present the crystal structure of the active CUB1CUB2 fragment of PCPE-1 bound to the C-propeptide trimer of procollagen III (CPIII). This shows that the two CUB domains bind to two different chains of CPIII and that the N-terminal region of one CPIII chain, close to the proteolytic cleavage site, lies in the cleft between CUB1 and CUB2. This suggests that enhancing activity involves unraveling of this chain from the rest of the trimer, thus facilitating the action of the proteinase involved. Support for this hypothesis comes from site-directed mutagenesis, enzyme assays, binding studies, and molecular modeling.

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

“…growth factor b [31,32]. The pCP activities of BMP1 are responsible for the cleavage of C-propeptides from procollagen precursors to produce mature collagen fibrils [33], which are promoted by some particular proteins including Procollagen C-Endopetidase Enhancer (PCPEs), sFRP2, and fibronectin [12][13][14]. PCPEs promote procollagen processing via a conformational change that renders procollagen a fitter substrate for pCP cleavage, while fibronectin and sFRP2 can directly bind to BMP1 to increase the cleavage activity [12][13][14].…”

“…After His-tagged sFRP2 was preincubated with FLAG-tagged PCPE1 for 4 h, and then incubated with His beads or FLAG beads for 2 h for immunoprecipitation (IP) and western blot analysis by anti-FLAG (A) and anti-His (B). PCPEs promote procollagen processing via a conformational change that renders procollagen a fitter substrate for pCP cleavage, while fibronectin and sFRP2 can directly bind to BMP1 to increase the cleavage activity [12][13][14]. growth factor b [31,32].…”

“…It contains a metalloproteinase domain, three CUB (complement/Uegf/BMP-1) domains, and an epidermal growth factor-like domain, and the CUB2 domain is essential for pCP activity [10,11]. 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].…”

Unraveling the Mechanism of Procollagen C-Proteinase Enhancer

“…In a collaboration between the Hulmes and Hohenester groups, the crystal structure of the human CPIII-C1C2 complex has been determined. While validating the SAXS model, the higher resolution of this structure has provided a more complete understanding of the mechanism of PCPE-1 enhancement of BMP-1 activity (Pulido et al, 2018). The beautiful flower structure of CPIII is immediately apparent and consistent with the CPIII structure in the absence of PCPE-1 (root-meansquare deviation [RMSD] of 1.25 Å between 669 a carbons) (Bourhis et al, 2013).…”

“…In this issue of Structure, Pulido et al (2018) determine the crystal structure of procollagen C-proteinase enhancer-1 (PCPE-1)/procollagen III complex and identify that PCPE-1 unwinds the stalk of the procollagen III trimer, liberating a single chain to facilitate binding and cleavage by BMP-1 proteinases for subsequent fibrillar collagen assembly.…”