Identification and characterization of a nucleotide binding site of ovine prolactin with 2-azido-NAD

Photo-immobilization of proteins on carbons

The photofunctionalization of three different carbons with two proteins was studied at room temperature. Water solutions of bovine serum albumin, BSA, and α-amylase, AA, were photolyzed at 21 °C in the presence of graphite microparticles (6.20 μm), MPG, graphene oxide, MPGO, and graphene oxide modified with SO₂, mMPGO. The insertion of BSA on carbon matrixes occurred with a deoxygenation reaction, most likely due to a dehydration step of a water molecule. XPS, TOC and TGA, showed that the BSA photo-insertion on MPG was highly efficient with 34.9% of the weight of MPG after photolysis, with an initial concentration of 1 g∙L^-1 of BSA. A high yield of AA photoinsertion on the carbons was also obtained. The calculated weight of AA inserted on MPG and MPGO after photolysis was 22.30% and 18.08%, respectively, with respect to the initial weight of carbon, when the initial concentration of AA was 60 mg∙L^-1. AA immobilized on MPG was active while the enzyme on MPGO showed a smaller activity, within the experimental error. Although a certain extent of denaturalization of both proteins was observed during photolysis, the molecular weight and composition changed very little during the photolysis, which would produce mainly conformational changes and isomerization reactions.

Characterization of a 2',5'-oligoadenylate (2-5A)-dependent 37-kDa RNase L: azido photoaffinity labeling and 2-5A-dependent activation

Upregulation of key components of the 2',5'-oligoadenylate (2-5A) synthetase/RNase L pathway has been identified in extracts of peripheral blood mononuclear cells from individuals with chronic fatigue [corrected] syndrome, including the presence of a low molecular weight form of RNase L. In this study, analysis of 2',5'-Oligoadenylate (2-5A) binding and activation of the 80- and 37-kDa forms of RNase L has been completed utilizing photolabeling/immunoprecipitation and affinity assays, respectively. Saturation of photolabeling of the 80- and the 37-kDa RNase L with the 2-5A azido photoprobe, [(32)P]pApAp(8-azidoA), was achieved. Half-maximal photoinsertion of [(32)P]pApAp(8-azidoA) occurred at 3.7 x 10(-8) m for the 80-kDa RNase L and at 6.3 x 10(-8) m for the 37-kDa RNase L. Competition experiments using 100-fold excess unlabeled 2-5A photoaffinity probe, pApAp(8-azidoA), and authentic 2-5A (p(3)A(3)) resulted in complete protection against photolabeling, demonstrating that [(32)P]pApAp(8-azidoA) binds specifically to the 2-5A-binding site of the 80- and 37-kDa RNase L. The rate of RNA hydrolysis by the 37-kDa RNase L was three times faster than the 80-kDa RNase L. The data obtained from these 2-5A binding and 2-5A-dependent activation studies demonstrate the utility of [(32)P]pApAp(8-azidoA) for the detection of the 37-kDa RNase L in peripheral blood mononuclear cell extracts.

The resonant recognition model (RRM) predicts amino acid residues in highly conserved regions of the hormone prolactin (PRL)

The resonant recognition model (RRM) is a model which treats the protein sequence as a discrete signal. It has been shown previously that certain periodicities (frequencies) in this signal characterise protein biological function. The RRM was employed to determine the characteristic frequencies of the hormone prolactin (PRL), and to identify amino acids ('hot spots') mostly contributing to these frequencies and thus proposed to mostly contribute to the biological function. The predicted 'hot spot' amino acids, Phe-19, Ser-26, Ser-33, Phe-37, Phe-40, Gly-47, Gly-49, Phe-50, Ser-61, Gly-129, Arg-176, Arg-177, Cys-191 and Arg-192 are found in the highly conserved amino-terminal and C-terminus regions of PRL. Our predictions agree with previous experimentally tested residues by site-direct mutagenesis and photoaffinity labelling.

Photoaffinity labelling of human poly(ADP-ribose) polymerase catalytic domain

Photoaffinity labelling of the human poly(ADP-ribose) polymerase (PARP) catalytic domain (40 kDa) with the NAD+ photoaffinity analogue 2-azido-[alpha-32P]NAD+ has been used to identify NAD+-binding residues. In the presence of UV, photo-insertion of the analogue was observed with a stoichiometry of 0.73 mol of 2-azido-[alpha-32P]NAD+ per mol of catalytic domain. Competition experiments indicated that 3-aminobenzamide strongly protected the insertion site. Residues binding the adenine ring of NAD+ were identified by trypsin digestion and boronate affinity chromatography in combination with reverse-phase HPLC. Two major NAD+-binding residues, Trp1014 of peptide Thr1011-Trp1014 and Lys893 of peptide Ile979-Lys893, were identified. The site-directed mutagenesis of these two residues revealed that Lys893, but not Trp1014, is critical for activity. The close positioning of Lys893 near the adenine ring of NAD+ has been confirmed by the recently solved crystallographic structure of the chicken PARP catalytic domain [Ruf, Menissier-de Murcia, de Murcia and Schulz (1996) Proc. Natl. Acad. Sci. U.S.A. 93, 7481-7485].

Identification of adenine binding domain peptides of the NADP+ active site within porcine heart NADP(+)-dependent isocitrate dehydrogenase

Photoaffinity labeling with [2'-32P]2N3NADP+ and [32P]2N3NAD+ was used to identify two overlapping tryptic and chymotryptic generated peptides within the adenine binding domain of NADP(+)-dependent isocitrate dehydrogenase (IDH). Photolysis was required for insertion of radiolabel, and prior photolysis of photoprobes before addition of IDH prevented insertion. Photoincorportion of 2N3NAD+ inhibited the enzymatic activity of IDH. Photolabeling of IDH with both [32P]2N3NAD+ and [2'-32P]2N3-NADP+ showed saturation effects with apparent Kds of 20 and 14 microM (+/-12%), respectively. The efficiency of photoincorporation at saturation of binding sites was determined to be about 50%. Also, photolabeling was observed with [32P]8N3ATP and [32P]2N3ATP but with saturation effects observed at lower affinity. With all radiolabeled probes reduction of photoinsertion was effected best by the addition of NADP+ followed by NAD+ and then ATP, indicating that photoinsertion with all the probes was within the NADP+ binding site. Isolation of [32P]2N3NAD+ and [2'-32P]2N3NADP+ photolabeled peptides by use of immobilized boronate and immobilized Al3+ chromatography, respectively, followed by HPLC purification resulted in the identification of overlapping peptides corresponding to Ile244-Arg249 and Leu121-Arg133 (tryptic fragments) and Lys243-His248 and Leu121-His135 (chymotryptic fragments). Trp125 and Trp245 were identified as the sites of photoinsertion based on these residues not being detectable on sequencing, the lack of chymotryptic cleavage at these residues, and the decreased rate of trypsin digestion at nearby Lys243 and Lys127. Sequence analysis of [32P]8N3ATP and [32P]2N3ATP photolabeled peptides gave essentially the same peptide regions being photolabeled but at much lower efficiency, indicating that the effects of ATP on IDH activity are dependent on competition for the same site.

Selective labeling of membrane protein sulfhydryl groups with methanethiosulfonate spin label

Electron paramagnetic resonance was used to characterize the first use of a thio-specific spin label in membranes. Procedures for use of the spin-label, 1-oxyl-2,2,5,5-tetramethyl-delta 3-pyrroline-3-methyl (methanethiosulfonate MTS) covalently attached to membrane proteins in human erythrocyte membranes are reported. The major findings are: (1) MTS was found to be thiol-specific in membranes as it is for soluble proteins; (2) MTS labels ghost proteins in as few as 30 min at room temperature, providing a distinct advantage when sensitive or fragile membranes are to be used; (3) the distribution of the spin label suggests that the major cytoskeletal protein, spectrin, and the major transmembrane protein (Band 3) incorporate the highest percentage of spin label. This procedure expands the tools with which the researcher can investigate the physical state of membrane proteins and its alteration upon interaction of membrane perturbants or in pathological conditions.