15N NMR relaxation data reveal significant chemical exchange broadening in the alpha-domain of human α-lactalbumin

Human alpha-lactalbumin (alpha-LA), a 123-residue calcium-binding protein, has been studied using (15)N NMR relaxation methods in order to characterize backbone dynamics of the native state at the level of individual residues. Relaxation data were collected at three magnetic field strengths and analyzed using the model-free formalism of Lipari and Szabo. The order parameters derived from this analysis are generally high, indicating a rigid backbone. A total of 46 residues required an exchange contribution to T(2); 43 of these residues are located in the alpha-domain of the protein. The largest exchange contributions are observed in the A-, B-, D-, and C-terminal 3(10)-helices of the alpha-domain; these residues have been shown previously to form a highly stable core in the alpha-LA molten globule. The observed exchange broadening, along with previous hydrogen/deuterium amide exchange data, suggests that this part of the alpha-domain may undergo a local structural transition between the well-ordered native structure and a less-ordered molten-globule-like structure.

The evolutionarily conserved transcription factor PRDM12 controls sensory neuron development and pain perception

PR homology domain-containing member 12 (PRDM12) is a highly evolutionary conserved member of the Prdm family of transcription factors that play essential roles in many cell fate decisions. In human, PRDM12 coding mutations have been recently identified in several patients with hereditary sensory and autonomic neuropathy (HSAN) (submitted elsewhere). Here we show that PRDM12 is involved in sensory neurogenesis in Xenopus and that several of the human Prdm12 mutants show altered structure, subcellular localization and function. In Drosophila, we demonstrate that the sensory neuron specific RNAi knockdown of the Prdm12 ortholog Hamlet induces impaired nociception and that a similar phenotype is observed in hypomorph hamlet mutants. In human fibroblasts of patients with PRDM12 mutations, we identified additional possible downstream target genes including thyrotropin-releasing hormone degrading enzyme (TRHDE). Knock-down of fly TRHDE in sensory neurons resulted in altered nociceptive neurons and impaired nociception. Collectively, these findings provide the first evidence showing that Prdm12 plays an important role in sensory neuron development. They also suggest that it has a critical evolutionarily conserved role in pain perception via modulation of the TRH signaling pathway.