Assembly of the Type 1 Procollagen Molecule:  Selectivity of the Interactions between the α1(Ι)- and α2(Ι)-Carboxyl Propeptides

Type I procollagen is a heterotrimer composed of two pro␣1(I) chains and one pro␣2(I) chain, encoded by the COL1A1 and COL1A2 genes, respectively. Mutations in these genes usually lead to dominantly inherited forms of osteogenesis imperfecta (OI) by altering the triple helical domains, but a few affect sequences in the pro␣1(I) C-terminal propeptide (C-propeptide), and one, which has a phenotype only in homozygotes, alters the pro␣2(I) C-propeptide. Here we describe four dominant mutations in the COL1A2 gene that alter sequences of the pro␣2(I) C-propeptide in individuals with clinical features of a milder form of the disease, OI type IV. Three of the four appear to interfere with disulfide bonds that stabilize the C-propeptide conformation and its interaction with other chains in the trimer. Cultured cells synthesized pro␣2(I) chains that were slow to assemble with pro␣1(I) chains to form heterotrimers and that were retained intracellularly. Some alterations led to the uncharacteristic formation of pro␣1(I) homotrimers. These findings show that the C-propeptide of pro␣2(I), like that of the pro␣1(I) C-propeptide, is essential for efficient assembly of type I procollagen heterotrimers. The milder OI phenotypes likely reflect a diminished amount of normal type I procollagen, small populations of overmodified heterotrimers, and pro␣1(I) homotrimers that are compatible with normal skeletal growth. Osteogenesis imperfecta (OI)4 (1, 2), commonly known as brittle bone disease, is usually caused by mutations in the COL1A1 and COL1A2 genes that encode the pro␣1(I) and pro␣2(I) chains, respectively, of type I procollagen. This heterotrimeric collagen is composed of two pro␣1(I) chains and one pro␣2(I) chain. Molecular assembly of the trimer is a multistep process that occurs following synthesis of the full-length chains and release from the ribosome. The C-terminal propeptide (C-propeptide) of each chain folds into a structure that is stabilized by intra-chain disulfide bonds and exposes a chain selectivity domain (3) that directs the interaction of the correct three chains into trimers. Following stabilization of the trimer by inter-chain disulfide bonds, the collagen triple helical domains are nucleated by sequences at their C-terminal end and the helix then propagates in an N-terminal direction.The vast majority of OI-causing mutations (4, 5) 5 affect the triple helical domains and perturb either the nucleation or the propagation of the triple helix N-terminal to the altered sequence but do not affect initial assembly of the pro␣ chains (6). The delay in helix propagation permits prolonged access of modifying enzymes to the chains N-terminal of the alteration (7), whereas the sequence alterations themselves alter the helical structure (8, 9) and reduce molecular thermal stability (10, 11). The phenotypic outcome of these mutations is, in part, due to the synthesis of structurally altered triple helices, and reflects both the location and nature of the change. These mutations result in the full spectrum of OI severity,...

Section: Discussionmentioning

confidence: 99%

Defective C-propeptides of the Proα2(I) Chain of Type I Procollagen Impede Molecular Assembly and Result in Osteogenesis Imperfecta

Pace

Wiese

Drenguis

et al. 2008

“…Furthermore, because intrachain disulfide bonding occurs between cysteines 83 and 245 and between cysteines 153 and 198, it can be speculated that each major lobe is stabilized by the Cys-153-Cys-198 pair, whereas each polypeptide chain is folded back on itself so that the Cys-83-Cys-245 bond is near the junction region. This interpretation is inspired by recent ab initio modeling studies on the procollagen I C-propeptide trimer (54). In addition, the model requires that the previously identified (30) discontinuous molecular recognition sequence involved in typespecific chain association (residues 122-133 and 142-144) be within the junction region.…”

Section: Discussionmentioning

confidence: 99%

Biophysical Characterization of the C-propeptide Trimer from Human Procollagen III Reveals a Tri-lobed Structure

Bernocco¹,

Finet²,

Ebel³

et al. 2001

Procollagen C-propeptide domains direct chain association during intracellular assembly of procollagen molecules. In addition, they control collagen solubility during extracellular proteolytic processing and fibril formation and interact with cell surface receptors and extracellular matrix components involved in feedback inhibition, mineralization, cell growth arrest, and chemotaxis. At present, three-dimensional structural information for the C-propeptides, which would help to understand the underlying molecular mechanisms, is lacking. Here we have carried out a biophysical study of the recombinant C-propeptide trimer from human procollagen III using laser light scattering, analytical ultracentrifugation, and small angle x-ray scattering. The results show that the trimer is an elongated molecule, which by modeling of the x-ray scattering data appears to be cruciform in shape with three large lobes and one minor lobe. We speculate that each of the major lobes corresponds to one of the three component polypeptide chains, which come together in a junction region to connect to the rest of the procollagen molecule.Fibril-forming collagens (types I, II, III, V, and XI) are synthesized and secreted into the extracellular matrix in precursor form, procollagens (ϳ500 kDa), with large N-and C-terminal propeptide regions (1). The propeptides increase the solubility of the procollagen molecule, thus preventing premature fibril formation inside the cell (2). After secretion, propeptides are cleaved to varying extents by specific procollagen N-and Cproteinases (3-5) and also other proteinases (6, 7), thereby triggering fibril assembly of collagen. Once cleaved, both Nand C-propeptides are thought to control further collagen synthesis by a process of feedback inhibition (8 -11). Also, in the extracellular matrix, the N-propeptides are involved in growth factor signaling (12), whereas the C-propeptides have been implicated in interactions with procollagen C-proteinase enhancer (13), mineralization (14 -16), integrin receptor binding (17, 18), cell growth arrest (19), and chemotaxis (20).In addition to their extracellular roles, numerous observations demonstrate the importance of the C-propeptide domain in chaperone-assisted chain association during intracellular assembly of procollagen molecules (21-24). Each procollagen molecule consists of three polypeptide chains encoded by one or more genes, giving rise to homotrimers or heterotrimers, respectively, with specific chain stoichiometries. For example, procollagen III molecules are homotrimers with the chain composition pro␣1(III) 3 , whereas procollagen I molecules are normally heterotrimers of the form pro␣1(I) 2 pro␣2(I). The C-propeptides direct association within the rough endoplasmic reticulum to ensure correct chain stoichiometry, which is particularly important in cells producing more than one procollagen type. Once associated into a trimer, and after prolyl hydroxylation, triple helix formation within the collagenous region is initiated at the C terminus and proceeds ...

“…The putative conformation and energy-minimized structures of the human ␣1 C-NC and ␣2 C-NC reveal (21,22) that each contains five subdomains ( Fig. 1A) (8,23).…”

Section: Fibril-forming Collagensmentioning

confidence: 99%

Molecular Recognition in the Assembly of Collagens: Terminal Noncollagenous Domains Are Key Recognition Modules in the Formation of Triple Helical Protomers

Khoshnoodi

Cartailler²,

Alvares

et al. 2006

Self Cite

181

145

The ␣-chains of the collagen superfamily are encoded with information that specifies self-assembly into fibrils, microfibrils, and networks that have diverse functions in the extracellular matrix. A key self-organizing step, common to all collagen types, is trimerization that selects, binds, and registers cognate ␣-chains for assembly of triple helical protomers that subsequently oligomerize into specific suprastructures. In this article, we review recent findings on the mechanism of chain selection and infer that terminal noncollagenous domains function as recognition modules in trimerization and are therefore key determinants of specificity in the assembly of suprastructures. This mechanism is also illustrated with computer-generated animations.Collagens are modular triple helical proteins that constitute the major structural components of the extracellular matrix of all animals. They occur as diverse suprastructures such as fibrils, microfibrils, and networks, which serve as self-organizing scaffolds for the attachment of other macromolecular complexes including laminin networks, proteoglycans, and cell surface receptors. The suprastructures play functional roles in cell adhesion, cell differentiation, tissue development, and the structural integrity of organs.Collagen suprastructures are assembled from a large family of gene products called ␣-chains. To date, 43 unique ␣-chains that belong to 28 types of collagens (types I-XXVIII) have been discovered in vertebrates. Based on their supramolecular architectures, they are further classified as fibril-forming, fibril-associated containing interrupted triple helices (FACIT), 3 beaded filament, anchoring fibril, network-forming, and transmembrane collagens (1-4). The assembly of all collagen suprastructures begins with the association of three type-specific ␣-chains (trimerization) that subsequently intertwine to form triple helical protomers, the building blocks of larger assemblies (1-5). Protomers are homotrimers or heterotrimers, composed of up to three different ␣-chains. They have in common at least one triple helical collagenous domain of varying length and two noncollagenous domains (NC) of variable sequence, size, and shape that are positioned at the N and C termini, designated herein as N-NC and C-NC domains, respectively. The terminal NC domains are excised, modified, or incorporated directly into the final suprastructure, depending on protomer type and function. Subsequently, specific protomers oligomerize into distinct suprastructures involving interactions that form end-to-end connections, lateral associations, and supercoiling of helices. Thus, protomer formation and oligomerization involve pivotal recognitions steps that target specific ␣-chains to assemble into a particular type of suprastructure.How the ␣-chains selectively recognize each other is a fundamental question in matrix biology that remains largely unanswered. Early studies on collagens I and III suggested that the C-NC domains play a critical role in the trimerization step that involv...