Deuteration protects asparagine residues against racemization

Racemization in proteins and peptides at sites of L-asparaginyl and L-aspartyl residues contributes to their spontaneous degradation, especially in the biological aging process. Amino acid racemization involves deprotonation of the alpha carbon and replacement of the proton in the opposite stereoconfiguration; this reaction is much faster for aspartate/asparagine than for other amino acids because these residues form a succinimide ring in which resonance stabilizes the carbanion resulting from proton loss. To determine if the replacement of the hydrogen atom on the alpha carbon with a deuterium atom might decrease the rate of racemization and thus stabilize polypeptides, we synthesized a hexapeptide, VYPNGA, in which the three carbon-bound protons in the asparaginyl residue were replaced with deuterium atoms. Upon incubation of this peptide in pH 7.4 buffer at 37 °C, we found that the rate of deamidation via the succinimide intermediate was unchanged by the presence of the deuterium atoms. However, the accumulation of the D-aspartyl and D-isoaspartyl forms resulting from racemization and hydrolysis of the succinimide was decreased more than five-fold in the deuterated peptide over a 20 day incubation at physiological temperature and pH. Additionally, we found that the succinimide intermediate arising from the degradation of the deuterated asparaginyl peptide was slightly less likely to open to the isoaspartyl configuration than was the protonated succinimide. These findings suggest that the kinetic isotope effect resulting from the presence of deuteriums in asparagine residues can limit the accumulation of at least some of the degradation products that arise as peptides and proteins age

Different Parasite Faunas in Sympatric Populations of Sister Hedgehog Species in a Secondary Contact Zone

<div><p>Providing descriptive data on parasite diversity and load in sister species is a first step in addressing the role of host-parasite coevolution in the speciation process. In this study we compare the parasite faunas of the closely related hedgehog species <i>Erinaceus europaeus</i> and <i>E. roumanicus</i> from the Czech Republic where both occur in limited sympatry. We examined 109 hedgehogs from 21 localities within this secondary contact zone. Three species of ectoparasites and nine species of endoparasites were recorded. Significantly higher abundances and prevalences were found for <i>Capillaria</i> spp. and <i>Brachylaemus erinacei</i> in <i>E. europaeus</i> compared to <i>E. roumanicus</i> and higher mean infection rates and prevalences for <i>Hymenolepis erinacei</i>, <i>Physaloptera clausa</i> and <i>Nephridiorhynchus major</i> in <i>E. roumanicus</i> compared to <i>E. europaeus</i>. Divergence in the composition of the parasite fauna, except for <i>Capillaria</i> spp., which seem to be very unspecific, may be related to the complicated demography of their hosts connected with Pleistocene climate oscillations and consequent range dynamics. The fact that all parasite species with different abundances in <i>E. europaeus</i> and <i>E. roumanicus</i> belong to intestinal forms indicates a possible diversification of trophic niches between both sister hedgehog species.</p></div