Structural properties of the methionine-containing subfraction of rat liver histone H1

Purification of histone H1 polypeptides by high-performance cation-exchange chromatography

Calf thymus histone 1 (H1) was cleaved by chemical and enzymatic methods and the resulting polypeptides were fractionated by high-performance cation-exchange. Up to 1 mg of H1 polypeptides were loaded onto a 50 x 5 mm I.D. cation-exchange column and fractionated to greater than 95% purity in less than 30 min. This is the first report on the separation of H1 polypeptides by a strong cation-exchange matrix. In addition, the high-performance cation-exchange chromatography protocol represents a significant decrease in fractionation time when compared to conventional ion-exchange and gel filtration chromatography. The utility of this procedure is shown when the H1 peptides purified by the protocol were used to define antigenic domains of H1 band by procainamide-induced lupus and idiopathic systemic lupus erythematosus. The majority of the sera tested by enzyme-linked immunoassay (ELISA) reacted to the C-terminal peptides of H1 indicating this to be the major antigenic domain of H1.

Histone H1 structure probed by Staphylococcus aureus V8-proteinase

Proteolytic digestion of calf thymus histone H1 with Staphylococcus aureus V8-proteinase under structuring conditions generates one major limit peptide P1 which consists of approx. 170 residues. Edman degradation establishes the N-terminal sequence as: Leu-Ile-Thr-Lys-Ala-Val-Ala-Ala-Ser-Lys. Chymotryptic fingerprinting shows that the C-terminal part of the H1 molecule is fully preserved. The peptide therefore comprises the residues H1 (42-210). The Glu-41 cleavage is extremely unusual as it occurs in the structured G-domain which is known to be resistant to proteinases (Hartman, P. G., Chapman, G. E., Moss, T. and Bradbury, E. M. (1977) Eur. J. Biochem. 77, 45-71; Böhm, L., Sautière, P., Cary, P. D. and Crane-Robinson, C. (1982) Biochem. J. 203, 577-582). The V8-proteinase cleavage product H1 (42-210) shows only 20% folding as compared to 95-99% folding shown by the peptides H1 (34-121), H1 (31-210) and H1 (33-210). Folding of the G-domain thus critically depends upon the presence of the eight residues 33-41 amongst which the Gly-Pro-Pro sequence at position 36-38 and a beta-turn predicted at position 35 are considered to be particularly important. The location of the cleavage site in the G-domain renders Staphylococcus aureus V8-proteinase suitable as a structural probe.