Human procollagen: I. An anionic tropocollagen precursor from skin fibroblasts in culture

Abstract

Tropocollagen is derived from an extracellular precursor, procollagen. Conversion to tropocollagen is accomplished by one or more tissue pioteases dependent in vitro on the presence of serum in the culture medium. Twenty-four hour cultures in which serum has been excluded yield an apparently undegraded precursor, procollagen I. The latter is approximately twice the size of tropocollagen, possesses an acidic pl in contrast to the alkaline pl of tropocollagen, and shares secondary structural characteristics common to tropocollagen. Procollagen I exhibits a sharp thermal transition point at 39° with a Δ T of 2° indicating that the collagenous portion of the molecule is in the triple helical configuration prior to proteolytic excision from the parent molecule. The amino acid composition is remarkable when compared to tropocollagen in the large quantity of acidic residues, decreased glycine and imino acids, and the presence of cystcine. Three models of procollagen I structure are presented and discussed relative to the available experimental evidence.