Solid-state conformation of some basic sequential polypeptides

We have studied the structure of solid films obtained by x-ray diffraction, from several basic polypeptides with a defined sequence. The alterating polypeptides poly(Ala-Lys), poly(Leu-Lys), poly(Val-Lys), and poly(Arg-Leu) all show a cross-β-structure in which layers of hydrophilic side chains alternate with layers containing hydrophobic side chains. The other polypeptides studied are not in the β-conformation and appear to be in the α-helical conformation. The helices obtained from poly(Lys-Ala-Ala) and poly(Lys-Ala-Ala-Lys) appear to be packed in an unusual fashion, which favors interaction between alanine side chains. Such behavior is not found in poly(Lys-Leu-Ala).     

Influence of basic polypeptides on the phase transition of phospholipid liposomes

Interaction of basic polypeptides (copolymers of lysine with phenylalanine or tyrosine) with phosphatidyserine or dipalmitoyl phosphatidylcholine liposomes was investigated by differential scanning calorimetry. The polypeptides cause a decrease in enthalpy of melting of the phospholipids almost without affecting the midpoint melting temperature.     

Interaction of bilayers with basic polypeptides

Summary The interaction of bilayers formed from glyceryl monooleate+oleic acid with basic polypeptides was studied. Copolymers of lysine with different amino acids interact with the bilayers reducing their resistance and increasing their capacitance.The largest effect was observed with the copolymerl-lysine/l-phenylalanine (1.41) which decreases the specific resistance by more than 3 orders of magnitude. The smallest effects on the resistance were obtained with the very hydrophilic copolymer ofl-lysine/l-serine (1.11). The contribution of the double-layer potential to the measured transmembrane potentials of the charged bilayers is considered and calculated for the case of the membrane containing dissociable components in the absence of interacting copolymers.     

Interaction of basic polypeptides with phospholipid monolayers

Adsorption of the polylysine and of the copolypeptides: L-lysine/L-serine and L-lysine/L-phenylalanine on phospholipid monolayers has been investigated. The charge density of the monolayers was varied by using the negatively charged phosphatidyl serine and the neutral phosphatidyl choline at different ratios. The surface concentrations of the adsorbed polypeptides was determined by measuring the surface radiation of their radioactive label.The adsorbing capacity of the monolayer surfaces increases with their negative charge, however with respect to polypeptides the surface activity sequence is pL < pLS < pLφ. From the dependence of adsorption on the ionic strength it was concluded that it is controlled by three types of interaction: (1) electrostatic attraction to the negatively charged surface; (2) electrostatic repulsion between adsorbed polybases; (3) hydrophobic interactions involving specific structural arrangements. This is true even of the apparently neutral PC monolayer where the fixed phosphate groups form an electrical double layer with the more mobile choline groups which can be interpenetrated by the charged groups of the basic polypeptides.     

Strongly basic polypeptides among microtubule associated proteins

Isoelectrofocussing between pH 3.5 and 9.5, or 9 and 11 in the first direction of two-dimensional gel electrophoreses reveal that the bands of microtubule associated proteins, e.g. the high molecular weight proteins and the τ factor, contain several polypeptides. A distinct group of these associated proteins possesses an isoelectric point of 9.5, and molecular weights between 72000 and 280000 daltons. This family of basic proteins is not the result of proteolytic cleavage of one high molecular weight precursor, as could be shown by fingerprint methods. A separation of native MAPS is briefly described.     

Influence of secondary structure of polyglycine on some conformational properties

Values of four conformational properties, namely unperturbed dimension [r2]0, dipole moment [mu 2], mean squared optical anisotropy [gamma 2], and molar Kerr constant [mK], have been calculated for polyglycine chains allowing several combinations of the secondary structure with the aim of studying the dependence of these magnitudes on the secondary structure of the chain. Two different approaches to the secondary structure have been used. In the first, chains with all their units in a given conformation (random coil, alpha-helix or beta-sheet) are interrupted at several positions by one unit in a different conformation. In the second, chains with varying composition of two conformations alpha-helix/beta-sheet and beta-sheet/random coil were allowed and the results obtained compared with previous work for alpha-helix/random coil chains.     

Biochemical properties of oncornavirus polypeptides

The major structural polypeptides of avian and mammalian oncornaviruses display a variety of unique physical and chemical properties. Techniques were designed to emphasize certain qualities of the individual proteins and glycoproteins which facilitate their identification in complex mixtures.     

Membrane polypeptides of some higher plant chloroplasts

Sodium dodecylsulfate-polyacrylamide gel electrophoresis of membrane polypeptides of the mesophyll cell chloroplasts of barley, pea, and maize show similar profiles, with the polypeptides falling into two major groups: those associated with a membrane fraction enriched in Photosystem I (called Group I polypeptides) and those associated with a membrane fraction enriched in Photosystem II (called Group II polypeptides a, b, and c). In contrast to these profiles, the polypeptides from the extensively unstacked membranes of chloroplasts from the chlorophyll-deficient mutant strains of barley and pea as well as those obtained from the agranal bundle sheath cell chloroplasts of maize are deficient in the Group II polypeptides b and c. It is proposed that these polypeptides are required for membrane stacking in higher plant chloroplasts.These Group II polypeptides b and c are not required for Photosystem II activity since both the barley and pea mutant chloroplasts and the maize bundle sheath chloroplasts possess Photosystem II activities.     

Inhibition of plant calcium-dependent protein kinases by basic polypeptides

Wheat embryo Ca2+-dependent protein kinase (CDPK) is inhibited by a variety of polypeptides including actin, gramicidin S, melittin, protamine, various histone preparations, histone H4 and by basic amino-acid homopolymers. Melittin (Ki 9 microM) is a non-competitive inhibitor of wheat germ CDPK and also inhibits wheat leaf CDPK and silver beet leaf CDPKs. Protamine inhibits wheat germ CDPK in an apparently competitive fashion (Ki 0.2 microM) and is also a potent, albeit less effective, inhibitor of the leaf CDPKs. Various basic amino-acid homopolymers are also potent, apparently competitive inhibitors of wheat embryo CDPK, namely poly(L-lysine) (IC50 2 nM), poly(L-ornithine) (IC50 3 nM) and poly(L-arginine) (IC50 17 nM) and also inhibit the leaf CDPKs, albeit at higher concentrations. Histone H4 and various calf thymus histone preparations inhibit wheat embryo CDPK in a fashion that is not competitive and calmodulin can substantially reverse such inhibition.     

Interactions of basic polypeptides and proteins with calmodulin.

Low concentrations (less than 10 microgram/ml) of a number of highly basic polypeptides inhibit the calmodulin-stimulated cyclic nucleotide phosphodiesterase. Inhibitory compounds include synthetic polypeptides [polylysine (D and L) and polyarginine] and basic proteins (protamine, histones H1, H2A, H2B, H3 and H4 and myelin basic protein). Polylysine of mol.wt. about 2000 or higher was inhibitory, but pentalysine did not inhibit. Other basic proteins and compounds did not inhibit, including bradykinin, spermine and putrescine. In mixtures of calmodulin and basic protein, complexes were formed whether Ca2+ was present or not. This was true for polylysine, myelin basic protein and histone H2B. These interactions suggest that the inhibition of the phosphodiesterase is due to interaction of these basic proteins with calmodulin. The wide variety of basic polypeptides and proteins that affect the calmodulin stimulation of phosphodiesterase indicates that these interactions are not specific.