The models of the denaturation of globular proteins. III. The intramolecular β-structure coil transitions in poly-S-carbobenzoxymethyl-l-cysteine

Conformational transitions in synthetic poly-S-carbobenzoxymethyl-l-cysteine (PCBMC) have been investigated in order to model the processes of the denaturation of globular proteins. The solutions of some samples of PCBMC in the mixtures of nonpolar solvents (dichloroethylene, chloroform) with highly polar solvents (dichloroacetic or trifluoroacetic acids) have been studied by viscosimetric, polarimetric, spectroscopic, and dielectric methods, as well as by light scattering and electronic microscopy. Intrinsic viscosity and levorotation increase sharply when solvent breaking hydrogen bonds are added in the narrow range of the solvent composition, the molecular weight (measured by light scattering) remaining constant. It means that intramolecular cooperative conformational transition occurs in the PCBMC molecules. The dispersion of optical activity shows the absence of the helical structures in PCBMC molecules for any solvent composition. Infrared spectra show that the PCBMC molecules possess β-structure in inert solvents and in films; and viscometric and polarimetric data suggest that this structure is an intramolecular one and corresponds to the compact shape of the PCBMC molecules in solution. The compact structure of PCBMC molecules in nonpolar solvents is also confirmed by dielectric data. The experimental results permit us to draw the conclusion that cooperative conformational transition involving intramolecular β-structure statistical coil occurs in PCBMC when solvent breaking hydrogen bonds are added. The position and the degree of sharpness of the transition do not depend on the molecular weight of the sample in the interval investigated (from 15,000 to 91,000). The “plate” model of the intramolecular β-structure has been proposed which does not contradict the results of the electron microscopic study. An assumption is made that owing to the two dimensional character of the intramolecular cross-β-structure its melting occurs in accordance with the “all-or-none” principle.

[1]  R. Fraser,et al.  AN INVESTIGATION OF THE STRUCTURE OF POLY-S-CARBOBENZOXY-L-CYSTEINE. , 1964, Journal of molecular biology.

[2]  H. F. Fisher,et al.  A LIMITING LAW RELATING THE SIZE AND SHAPE OF PROTEIN MOLECULES TO THEIR COMPOSITION. , 1964, Proceedings of the National Academy of Sciences of the United States of America.

[3]  E. Blout,et al.  AN ANALYSIS OF THE OPTICAL ROTATORY DISPERSION OF POLYPEPTIDES AND PROTEINS. II. , 1964, Proceedings of the National Academy of Sciences of the United States of America.

[4]  K. Imahori.  β‐Conformation in γ‐globulin , 1963 .

[5]  E. Katchalski,et al.  Synthesis, characterization, and acemization of poly-L-serine. , 1963, Biochemistry.

[6]  E. Bradbury,et al.  Optical rotatory dispersion and infrared studies of Beta-structures of Poly-O-benzyl-L-serine in solution. , 1962, Journal of molecular biology.

[7]  A. Wada,et al.  On the 1700 cm−1 band of the cross-β structure , 1961 .

[8]  A. Wada,et al.  OPTICAL ROTATORY DISPERSION OF THE β-FORM OF THE POLYPEPTIDE CHAIN , 1961 .

[9]  E. R. Blout,et al.  THE DEPENDENCE OF THE CONFORMATIONS OF SYNTHETIC POLYPEPTIDES ON AMINO ACID COMPOSITION1,2 , 1960 .

[10]  E. Blout,et al.  The Synthesis and the Conformation of Poly-L-serine and Poly-O-acetyl-L-serine1,2 , 1960 .

[11]  A. Keller.  The morphology of crystalline polymers , 1959 .

[12]  P. Doty,et al.  Polypeptides. IV. The Molecular Weight, Configuration and Association of Poly-γ-benzyl-L-glutamate in Various Solvents , 1956 .

[13]  E. Blout,et al.  Polypeptides. V. The Infrared Spectra of Polypeptides Derived from γ-Benzyl-L-glutamate , 1956 .

[14]  E. J. Ambrose,et al.  Infra-red spectra and structure of fibrous proteins , 1951, Proceedings of the Royal Society of London. Series A. Mathematical and Physical Sciences.

[15]  Ptitsyn Ob,et al.  [Synthesis of poly-S-carbobenzomethoxy-L-cysteine and studies on its structure]. , 1965 .

[16]  K. Hamaguchi.  STRUCTURE OF MURAMIDASE (LYSOZYME). 8. EFFECT OF DIMETHYL SULFOXIDE ON THE STABILITY OF MURAMIDASE. , 1964, Journal of biochemistry.

[17]  K. Imahori,et al.  An x‐ray examination of poly‐O‐acetyl‐L‐serine , 1963 .

[18]  K. Imahori,et al.  The “Cross-β” Structure in Poly-O-Acetyl-L-Serine , 1963 .

[19]  B. Harrap,et al.  POLY-S-CARBOBENZOXYMETHYL-L-CYSTEINE: A MODEL SYSTEM FOR THE DENATURATION OF NON-HELICAL PROTEINS. , 1963, Biochimica et biophysica acta.