Procollagen molecule

Processing of a newly synthesized type V procollagen molecule is also different from that of type I collagen. BMP-1, which is the C-propeptidase of type I, II, and III collagens, cleaves the N-terminal propeptide of the pro-al(V) chain, and a furin-like proteinase cleaves the C-terminal propeptide. The tyrosine residue in the N-terminal NC domain of type V collagen is sulfated. This modification might be related to... 

Transport of procollagen molecules from the ER to the Golgi was shown to occur in transport complexes and it... 

Extracellular cleavage of procollagen molecules After their release, the procollagen molecules are cleaved by N- and C-pro-collagen peptidases, which remove the terminal propeptides, releasing triple-helical collagen molecules. 

E. The procollagen molecule contains nonhelical C-and N-terminal extensions. 

Since fibril assembly can be regarded in part as a spontaneous self-assembly process, the limitation of fibril size could be ascribed to a physical equilibrium between soluble procollagen molecules and the growing insoluble fibril. Fibril-forming collagens are synthesized as precursor... 

Figure 5.7. Diagram showing role of N- and C-propeptides in collagen self-assembly. The procollagen molecule is represented by a straight line with bent (N-propeptide) and circular (C-propeptide) regions. Initial linear and lateral aggregation is promoted by the presence of both the N- and C-propeptides. In the presence of both propeptides lateral assembly is limited and the fibrils are narrow. Removal of the N-propeptide results in lateral assembly of narrow fibrils removal of the C-propeptide results in additional lateral growth of fibrils. As indicated in the diagram, the presence of the N- and C-propeptides physically interferes with fibril formation.

Question Once the procollagen molecule is hydroxylated, glycosylated, and coiled into a triple helix, how is it processed to form higher structures ... 

The procollagen molecule is secreted from the cell, and the extension propeptides are excised by two specific procollagen peptidases to form the tropocollagen molecule. The removal of the peptides (Mr = 20,000 and 35,000) allows the tropocollagen molecules to self-assemble to form fibrils. This assembly is regulated to some extent by the cells and by other extracellular components to produce the wide variety of structures found in collagen fibers. 

After the secretion into the extracellular space, collagen molecules may be modified chemically even more. Some collagen processing enzymes cleave the procollagen molecules to mature tissue type molecules. Lysine and 5-hydroxylysine residues can be modified enzymatically to allysine (alpha-aminoadipic-acid delta-semialdehyde) and hydroxyallysine (delta-hydroxy, alpha-aminoadipic acid delta-semialdehyde), respectively, by lysyl oxidase (protein-lysine 6-oxidase) (EC 1.4.3.13). The aldehyde group then interacts with the amino group of an adjacent lysine residue to form a Schiff base. Many... 

Collagen biosynthesis and secretion follow the normal pathway for a secreted protein, which is described in detail in Chapters 16 and 17. The collagen a chains are synthesized as longer precursors, called pro-a chains, by ribosomes attached to the endoplasmic reticulum (ER). The pro-a chains undergo a series of covalent modifications and fold into triple-helical procollagen molecules before their release from cells (Figure 6-20). 

The synthesis of fibrillar collagen (e.g., types I, II, and III) begins Inside the cell with the chemical modification of newly made a chains and their assembly Into triple-helical procollagen within the endoplasmic reticulum. After secretion, procollagen molecules are cleaved, associate laterally, and are covalently cross-linked Into bundles called fibrils, which can form larger assemblies called fibers (see Figure 6-20). 

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