D-Biotin p-nitrophenyl ester

The homotetrameric and biotin-binding properties of avidin and streptavidin have been exploited for a myriad of biotechnological applications and theoretical studies. Among the few differences between the two proteins is the capacity of avidin to hydrolyze biotinyl p-nitrophenyl ester (BNP), as opposed to streptavidin, which fully protects the same pseudosubstrate from hydrolysis. Combined mutagenesis and X-ray analysis have been used to attempt to understand this diametric difference in activities. It was found that a charged residue and one of the loops (L3,4) are together responsible for this difference. Recently, the avidin-related analogue AVR4 was found to have an even more pronounced BNP-hydrolysis activity than avidin. Again, the combination of charged residue(s) (Asp39 and/or Arg112) and the rigid conformation of the L3,4 loop was suggested to be responsible for the observed hydrolysis reaction. However, replacement of the latter charged residues in AVR4 resulted in only a modest reduction in hydrolytic activity at most, whereas replacement of the L3,4 loop of avidin with the rigid loop of AVR4 caused a dramatic increase in the activity of avidin. These results clearly demonstrate that the main feature responsible for the observed differences in rates of hydrolysis among the avidins is the conformational status of the L3,4 loop, which imposes conformational constraints on the pseudosubstrate, thereby rendering it susceptible to nucleophilic attack by solvent. In this context, the hydrolytic properties of the avidins reflect enzyme catalysis, in that subtleties in substrate binding are the determining features of catalytic efficiency.

N-hydroxysuccinimide (NHS) esters of biotin are reported to react specifically with amino groups of peptides and proteins. However, we have found that these reagents can readily acylate other functional groups in specific peptide sequences under relatively mild conditions. We have extended our inquiry of sequence-dependent acylation by evaluating the reactivity of a variety of commonly employed biotinylation reagents typically used for amino group modification. These included the p-nitrophenyl ester of biotin, NHS-esters of biotin containing aminohexanoic acid spacer arms, and a sulfonated NHS-biotin ester that contained a disulfide bond within its spacer. The decapeptide [D-Lys6]gonadotropin releasing hormone was employed as a model peptide. Reaction products were characterized by high-performance liquid chromatography, amino acid compositional analysis, reaction with hydroxylamine, and mass spectrometry. In addition to the O-acylation of Ser4 and Tyr5 in this peptide, we have also identified a novel biotinylation of the Arg8 side chain.

Biotin-labeled peptides are used for numerous biochemical and microbiological applications. Due to the strong affinity of biotin to streptavidin, the detection of biotinylated molecules is very sensitive. A powerful technique for parallel synthesis and high-throughput screening of peptides is the spot synthesis. One example for the use of spot synthesis is the screening of biotinylated peptides synthesized on cellulose membranes, which is particularly favorable for the investigation of protease cleavage sites. Additionally, in combination with biotinylated protein samples, the spot technique can be used for investigations of peptide-protein and protein-protein interactions. Here, we present our results of the use biotin p-nitrophenyl ester (biotin-ONp) in spot synthesis and as a reagent for biotin-labeling of protein samples.