Biochimica et Biophysica Acta (BBA) - Protein Structure最新文献

Coupling of peptides to protein carriers has been achieved at a high level of peptide incorporation. Bovine serum albumin was used as the model carrier protein and several peptides were tested in the coupling reaction. The peptides were coupled to succinylated bovine serum albumin after conversion of its caroxyl side chains to the reactive $\text{p-}\text{nitrophenyl}$ ester groups by reaction with $\text{p-}\text{nitrophenol}\text{/N,N′-}\text{dicyclohexylcarbodiimide}$ in anhydrous dimethylformamide. The reaction afforded succinyl-albumin-peptide conjugates that had high levels of peptide incorporation (18–35 mol peptide/mol albumin). In addition to the high level of peptide coupling, the reaction avoids the production of polymeric forms of peptide, protein or conjugate.

A method for covalent attachment of a fluorescent molecule to the carbohydrate moieties of glycoproteins is described. The glycoproteins were oxidized with periodate under mild conditions selective for sialic acid (Van Lenten, L. and Ashwell, G. (1971) J. Biol. Chem. 246, 1889–1894). The resulting aldehydes were condensed with either dansylhydrazine, dansylethylenediamine, or fluoresceinamine followed by reduction with NaCNBH₃ and NaBH₄. Conjugates prepared with dansylhydrazine were found to be insufficiently stable for spectroscopic analysis, whereas the primary amines produced stable conjugates whose fluorescence polarization ($\text{P}$) was constant for several hours at 37°C. The degree of labeling correlated roughly with the sialic acid contents of the vaious glycoproteins. Very little covalent incorporation was observed with albumin (which is devoid of carbohydrate) or with asialo $\text{α}{}_1\text{-}\text{acid}$ glycoprotein. Exclusion chromatography in the presence of a dissociating agent was sometimes required to remove significant amounts of noncovalently adsorbed dye. Fluorescent-labeled α subunits of human chorionic gonadotropin were shown to recombine normally with native β subunits. However, the labeling procedure appeared to compromise the ability of the β subunits to recombine. Electrophoretic analysis produced evidence of covalent cross-linking between subunits following periodate oxidation of the intact gonadotropin. The possibility that primary amine groups of the protein compete with added fluorescent amines for reaction with periodate-generated aldehydes is discussed.

Human lactotransferrin contains six residues of methionine per mol. Seven different fragments were characterized after treatment with cyanogen bromide (CNBr) and large parts of their sequences were determined. The alignment of the CNBr fragments was established by the determination of N- and C-terminal sequences, by the study of the C-terminal domain obtained by peptic digestion of the protein and by taking into account the internal homology as well as homology with human serum transferrin. The two glycopeptides were situated in the N- and C-terminal parts of the protein, respectively, a situation quite different from that encountered in serum transferrin. The sequence studies allowed us to suggest a 4- and perhaps 6-fold internal homology.

Resonance Raman spectra were observed for a mitochondria-type cytochrome $\text{P-450}$ ($\text{P-450}{}_{\mathrm{<mtext>SCC</mtext>}}$ for the first time. Reduced $\text{P-450}{}_{\mathrm{<mtext>SCC</mtext>}}$ at pH 7.4 exhibited the $\text{v}{}_4$ line at 1342 cm⁻¹, which is an unusually low frequency compared with an ordinary protohemoprotein but is common to the family of cytochrome $\text{P-450}$, suggesting the coordination of a strong π-donor such as thiolate anion at the fifth coordination position of the heme iron. The anomaly was preserved for the CO-complex of the reduced form. The $\text{v}{}_{10}$ line of oxidized $\text{P-450}{}_{\mathrm{<mtext>SCC</mtext>}}$ with a substrate was observed at 1617 cm⁻¹. This frequency and those of other structure-sensitive bands implied that the heme iron of oxidized $\text{P-450}{}_{\mathrm{<mtext>SCC</mtext>}}$ adopts the hexa-coordinate high-spin structure, in contrast with the high-spin type cytochrome $\text{P-450}$ purified from phenobarbital- or 3-methylcholanthrene-treated rabbit liver microsomes which presumably have a penta-coordinate structure. In the presence of 20α-hydroxycholestero, oxidized $\text{P-450}{}_{\mathrm{<mtext>SCC</mtext>}}$ gave the $\text{v}{}_{10}$ line at 1637 cm⁻¹, i.e., at a frequency similar to that of low-spin type cytochrome $\text{P-450}$. The alkaline-denatured $\text{P-450}{}_{\mathrm{<mtext>SCC</mtext>}}$ preparation in the presence of both dithiothreitol and EDTA, but not the $\text{P-450}{}_{\mathrm{<mtext>SCC</mtext>}}$ gave the $\text{v}{}_{10}$ line at 1637 cm⁻¹, i.e., at a frequency similar to that of low-spin type cytochrome $\text{P-450}$. The alkaline-denatured $\text{P-420}{}_{\mathrm{<mtext>SCC</mtext>}}$ preparation in the presence of both dithiothreitol and EDTA, but not the $\text{P-450}{}_{\mathrm{<mtext>SCC</mtext>}}$.

The protein composition of a well-defined α-granule preparation isolated from human platelets has been studied. Crossed immunoelectrophoresis against polyspecific platelet antibodies revealed more than 20 immunoprecipitates. The glycoprotein II_b-III_a complex represented a major antigen in the Triton X-100-solubilized α-granule preparation and cross-reacted with the corresponding platelet membrane antigen. Furthermore, after lactoperoxidase-catalyzed ¹²⁵I-iodination of whole platelets it was not labelled, in contrast to its membrane-located counterpart. This indicates an intracellular location of glycoproteins II_b and III_a, probably as constituents of the α-granules. Fibrinogen, platelet factor 4, albumin, factor VIII-related antigen and the main granule glycoprotein (thrombin-sensitive protein, thrombospondin) were identified in the α-granule preparation by the crossed immunoelectrophoresis technique. Crossed affinity immunoelectrophoresis using lectins revealed the presence of at least seven glycoproteins, and six sialoglycoproteins were identified by their altered electrophoretic mobility after neuraminidase treatment. Sodium dodecyl sulphate polyacrylamide gel electrophoresis of reduced samples of the α-granules revealed at least 15 Coomassie Brilliant Blue-staining polypeptide bands, one of which comigrated with myosin heavy chain. No prominent band was observed in the actin region. Five glycopolypeptide bands were obsevered after periodic acid-Schiff staining. The dominant three represented the main granule glycoprotein, glycoprotein II_b and glycoprotein III_a, respectively. More glycoproteins seem to be present in the α-granules than was previously recognized.

The primary structure of the C-terminal region (94 residues) of the ADP,ATP carrier of beef heart mitochondria is described. CNBr cleavage results in a large peptide (CB1) with $\text{M}{}_{\mathrm{<mtext>r</mtext>}}$ 22 000 and several small peptides (CB2 to CB8). Peptide separation was achieved by gel chromatography with 80% formic acid or with an ethanol/formic acid mixture. The amino acid sequence of the small CNBr peptides was determined by solid-phase techniques. Hydrolysis in formic acid cleaves the carrier protein into an $\text{M}{}_{\mathrm{<mtext>r</mtext>}}$ 23 000 fragment (A1) with the blocked N-terminus and an $\text{M}{}_{\mathrm{<mtext>r</mtext>}}$ 10 000 fragment (A2) starting with proline. The alignment of two CNBr fragments was possible by degradation of A2 by solid-phase methods for 34 steps. The remaining CNBr fragments were arranged by sequencing the tryptic peptides of citraconylated A2.

EPR spectra are reported for the multiheme enzyme hydroxylamine oxidoreductase of Nitrosomonas europaea. Signals arising from several different types of low-spin ($\text{S =}\text{1}\text{2}$) ferric heme were observed in the resting (oxidized) enzyme, but no evidence was obtained for high-spin ($\text{S =}\text{5}\text{2}$) heme, copper or iron-sulfur centers. While overlap of the low-spin heme signals at X-band frequency complicates complete assignment of $\text{g}$ values, four species with low field peaks at $\text{g}$ 3.4, 3.1, 3.0 and 2.7 were clearly resolved. Complete reduction of the enzyme with sodium dithionite abolished all major signals. Partial reduction of the enzyme by hydroxylamine caused disappearance of signals at $\text{g 3.1, g 2.22}$ and $\text{g 1.35}$ indicating selective reduction of this low-spin component by the substrate.

Kinetics of the reactions of Riftia pachyptila hemoglobin with oxygen were followed spectrophotometrically by stopped-flow and laser flash photolysis techniques. The rate of oxygen dissociation increases 8-fold over the range 5–20°C ($\text{k = 2.2}\text{s}{}^{\mathrm{-1}}\text{at}\text{10°}\text{C}$). Oxygen recombination following flash photolysis was biphasic. The rates of both slow and fast phases of the reaction were independent of temperature from 0 to 20°C ($\text{k}{}_{\mathrm{<mtext>fast</mtext>}}{}^{\mathrm{\prime }}\text{= 7 · 10}{}^6\text{; k}{}_{\mathrm{<mtext>slow</mtext>}}{}^{\mathrm{\prime }}\text{= 1 · 10}{}^6\text{1 ·}\text{mol}{}^{\mathrm{-1}}\text{·}\text{s}{}^{\mathrm{-1}}$). As the oxygen affinity is relatively temperature independent, analysis in terms of the two-state model of Monod, Wyman and Changeaux (1965, J. Mol. Biol. 12 88–118) requires that the conformational equilibrium constant L decrease by approx. 50-fold between 3 and 15°C.

Guinea pig liver transglutaminase has been used to incorporate putrescine into horse heart cytochrome $\text{c}$. The native protein showed essentially no incorporation, while ethanol-denatured cytochrome $\text{c}$ incorporated almost 1 mol putrescine per mol protein. No increase in this level of modification was obtained when maleylated cytochrome $\text{c}$ and the tryptic peptides of cytochrome $\text{c}$ were used as substrates. Analysis of the modified ethanol-denatured cytochrome $\text{c}$ by tryptic cleavage and peptide isolation showed that glutamine-42 of the intact protein is the site of incorporation of radioactively labelled putrescine. Ethanol-denatured cytochrome $\text{c}$ that was specifically modified at glutamine-42 by incorporation of putrescine could be readily renatured. The renatured modified protein showed reactivity with cytochrome $\text{c}$ oxidase comparable to that of the original native protein.