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PubMed2003

Genetic diversity and relationships of indigenous Kenyan camel (Camelus dromedarius) populations: implications for their classification.

The genetic diversity and relationships amongst the dromedary (Camelus dromedarius) populations are poorly documented. Four recognized Kenyan dromedary breeds (Somali, Turkana, Rendille, Gabbra) and dromedary from Pakistan and the Arabian Peninsula (Saudi Arabia, United Arab Emirates) were studied using 14 microsatellite loci. Phylogenetic analysis showed that Kenyan dromedaries are distinct from Arabian and Pakistani populations. Expected heterozygosity and allelic diversity values indicate that Kenyan dromedaries are less diverse than non-Kenyan populations. With the exception of the Somali population, the Kenyan dromedaries are poorly differentiated (average FST=0.009), with only one to two loci separating the Gabbra, Rendille and Turkana populations studied (P < 0.05). Individual assignments were performed using the maximum likelihood method. A correct breed assignment of only 39-48% was observed for the Kenyan dromedaries, using an allocation stringency of a log of the odds ratio >2. Our results do not support the present classification of the indigenous Kenyan dromedary into four distinct breeds based on socio-geographical criteria. Instead, our results point to just two separate genetic entities, the Somali and a group including the Gabbra, Rendille and Turkana populations.

Animals↗
PubMed2004

Chemical basis for the affinity maturation of a camel single domain antibody.

Affinity maturation of classic antibodies supposedly proceeds through the pre-organization of the reactive germ line conformational isomer. It is less evident to foresee how this can be accomplished by camelid heavy-chain antibodies lacking light chains. Although these antibodies are subjected to somatic hypermutation, their antigen-binding fragment consists of a single domain with restricted flexibility in favor of binding energy. An antigen-binding domain derived from a dromedary heavy-chain antibody, cAb-Lys3, accumulated five amino acid substitutions in CDR1 and CDR2 upon maturation against lysozyme. Three of these residues have hydrophobic side chains, replacing serines, and participate in the hydrophobic core of the CDR1 in the mature antibody, suggesting that conformational rearrangements might occur in this loop during maturation. However, transition state analysis of the binding kinetics of mature cAb-Lys3 and germ line variants show that the maturation of this antibody relies on events late in the reaction pathway. This is reflected by a limited perturbation of k(a) and a significantly decreased k(d) upon maturation. In addition, binding reactions and the maturation event are predominantly enthalpically driven. Therefore, maturation proceeds through the increase of favorable binding interactions, or by the reduction of the enthalpic penalty for desolvation, as opposed to large entropic penalties associated with conformational changes and structural plasticity. Furthermore, the crystal structure of the mutant with a restored germ line CDR2 sequence illustrates that the matured hydrophobic core of CDR1 in cAb-Lys3 might be compensated in the germ line precursor by burying solvent molecules engaged in a stable hydrogen-bonding network with CDR1 and CDR2.

Amino Acid Sequence↗