Denaturation-renaturation properties of two molecular forms of short-chain cartilage collagen

Certain physical properties of two molecular forms of short-chain (SC) cartilage collagen [Schmid, T. M., & Linsenmayer, T. F. (1983) J. Biol. Chem. 258, 9504-9509] have been determined. The 59K form has both a collagenous and a noncollagenous domain, and the 45K form has only the collagenous one. By circular dichroic spectropolarimetry, both forms show the characteristic spectrum of a collagen triple helix with a maximum ellipticity at 222 nm and a minimum at 197 nm. The denaturation temperature (Tm) of the helical structure of both forms, as monitored at 222 nm, is approximately 47 degrees C. Thus, the presence of the nonhelical domain does not greatly affect this property. After thermal denaturation, however, the renaturation of the 59K form is much more rapid than that of the 45K form, regaining greater than 60% of its helical structure within 40 min. The 45K form regains at most 15%, even after 24 h. Gel filtration on Sephacryl S-500, run under nondenaturation conditions, showed that the molecules renatured from the 59K form had regained a structure indistinguishable from native ones, while the 45K had not. The noncollagenous domain of the 59K form could be obtained by digestion with bacterial collagenase. This domain, as previously reported, contains no disulfide bonds. But, it is very stable, requiring both detergent and heating to separate its component chains. We hypothesize that the chains within this domain are tightly held together by strong, noncovalent forces, such as hydrophobic bonds, which are refractory to thermal denaturation. These maintain the chains in proper registry, thus facilitating rapid renaturation of the helical domain.