Food Biochemistry and Food Processing (2 edition)

BLBS102-c20 BLBS102-Simpson March 21, 2012 13:35 Trim: 276mm X 219mm Printer Name: Yet to Come

366 Part 3: Meat, Poultry and Seafoods

(C)

(A)

-Gly-X-Y-Gly-Pro-Hyp-Gly-X-Hyp-Gly-Pro-Y-

Intermolecular (D)

cross-links

Telopeptides

α-chain (B)

N-terminal C-terminal

Figure 20.1.Arrangement of collagen fibril in collagen fiber. (A) Amino acid sequence of a collagen polypeptide. (B) Collagen polypeptide.

(C) Tropocollagen. (D) Collagen fibril.

COLLAGEN COMPOSITION AND

STRUCTURE

Collagen is typically used as a generic term to cover a large fam-

ily of distinct proteins, each with specific structures, functions,

and tissue distributions in the extracellular matrix (Ramshaw

et al. 2009). The collagen monomer is a long cylindrical protein

about 2800 Å long and 14–15 Å in diameter (Foegeding et al.

1996). Collagen is constructed from tropocollagen, a rod-shaped

protein consisting of three polypeptides unit (calledα-chains)

intertwined to form a triple-helical structure. Eachα-chain coils

in a left-handed helix with three residues per turn, and the three

chains are twisted right-handed to form the triple helix (Wong

1989) (Fig. 20.1). The three chains are held together primarily

by hydrogen bonding between adjacent –CO and –NH group

(Wong 1989, Lee et al. 2001). At least 19 types of collagen des-

ignated types I–XIX have been reported (Bailey et al. 1998, Lee

et al. 2001, Woo et al. 2008). Differentα-chains, designatedα1,

α2, orα3, within the same type of collagen differ in their amino

acid composition. The distribution ofα1-,α2-, andα3-chains

in collagen molecules varies depending on the specific genetic

variants (Xiong 1997). The most common collagen is type I col-

lagen. It contains twoα1(I)-chains and oneα2(I)-chain, which

has different amino acid sequence and composition. Each chain

has a molecular mass about 100,000Da, yielding a total molecu-

lar mass of about 300,000 Da of collagen (Foegeding et al. 1996).

Type I collagen is the major of epimysium. Both types I and III

are present in the perimysium in large amounts, whereas types

II, IV, and V are primary species in epimysium (Table 20.1)

(Xiong 1997). Types I, II, and III collagen as well as types V

Table 20.1.Collagens and Their Distribution

Type Peptide Chainsa Molecular Composition Occurrence

I α1,α2[α1(I)] 2 α2(I) Skin, tendon, bone, muscle (epimysium)

II α1[α1(II)] 3 Intervertebral disc, cartilage

III α1[α1(III)] 3 Fetal skin, cardiovascular vessel, uterus, synovial membranes,

inner organ, muscle (perimysium)

IV α1,α2[α1(IV)] 3 (?)b Basement membrane, kidney glomeruli, lens capsule, glomeruli

V AA,αB,αC (?) [αB] 2 αAor(αB) 3 +

(αA) 3 or (αC) 3 (?)

Placental membrane, cardiovascular system, lung, muscle

(endomysium)

Sources: Wong (1989) and Belitz et al. (2004).

aSince theα-chains of various types of collagen differ, the are calledα1(I),α1(II),αA, etc.

b(?) Not completely elucidated.