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Biosynthesis of the ribosomally synthesized and post-translationally modified peptide (RiPP), pyrroloquinoline quinone (PQQ), is initiated when the precursor peptide, PqqA, is recognized and bound by the RiPP precursor peptide recognition element (RRE), PqqD, for presentation to the first enzyme in the pathway, PqqE. Unlike other RiPP-producing, postribosomal peptide synthesis (PRPS) pathways in which the RRE is a component domain of the first enzyme, PqqD is predominantly a separate scaffolding protein that forms a ternary complex with the precursor peptide and first tailoring enzyme. As PqqD is a stable, independent RRE, this makes the PQQ pathway an ideal PRPS model system for probing RRE interactions using nuclear magnetic resonance (NMR). Herein, we present both the solution NMR structure of Methylobacterium extorquens PqqD and results of 1H-15N HSQC binding experiments that identify the PqqD residues involved in binding the precursor peptide, PqqA, and the enzyme, PqqE. The reported structural model for an independent RRE, along with the mapped binding surfaces, will inform future efforts both to understand and to manipulate PRPS pathways.

Controlled proteolysis and photoaffinity labeling with azidonucleotide analogues, 8-azido-ATP and 5-azido-dUTP with or without dNTP competitor were performed to identify the regions of rat DNA polymerase beta (beta-pol) involved in nucleotide binding. Four proteolytic domains of 8, 6, 10 and 12 kDa which extend from the N-terminus to the C-terminus were identified. The 8 kDa domain and the 10 and 12 kDa subdomains were observed to constitute the dNTP binding pocket.

The rate of iron release from the H249Y N-lobe mutant of human transferrin is much higher than the release from other mutants such as R124S, R124K, K206R, H207E, and Y95H. Iron release from the N-lobe K206 and H207 mutants is very slow compared to the iron release from wild-type N-lobe. The mutation of R124 accentuates iron release both at the endosomal pH of 5.6 and at extracellular pH of 7.4. A simple model that accounts for the negative effect of N-lobe iron release is presented.

Examines a study which found that there is a vigorous tryspin digestion of 27KDA fragment produces 10 and 12 KDA subdomains. Relative photochemical labeling of regions of DNA polymerase.