Oxytocin

Substantial excitement surrounds the mammalian peptide hormone oxytocin (OT) due to its potential to be a “hormone of love”—and more generally, a biological foundation for the diverse classes of intimate social bonds. Yet, theoretical models have struggled to absorb inconsistent, even contradictory, findings. Evolutionary theory will guide a coherent functional interpretation of the OT system. This chapter focuses on life history theory, a branch of theoretical biology that seeks to identify how natural selection shapes organisms’ efforts to optimally allocate limited resources. Endocrine hormones are important mediators of this process. A review of the psychological and physiological literature regarding OT suggests a number of possible trade-offs negotiated by oxytocinergic activity. This chapter proposes a provisional life history model in which OT is central to the regulation of important but vulnerable social relationships. It outlines implications of this model, addresses a number of caveats, and suggests directions for future research.

Glutaminyl cyclases from animals and plants: a case of functionally convergent protein evolution

Several mammalian peptide hormones and proteins from plant and animal origin contain an N-terminal pyroglutamic acid (pGlu) residue. Frequently, the moiety is important in exerting biological function in either mediating interaction with receptors or stabilizing against N-terminal degradation. Glutaminyl cyclases (QCs) were isolated from different plants and animals catalyzing pGlu formation. The recent resolution of the 3D structures of Carica papaya and human QCs clearly supports different evolutionary origins of the proteins, which is also reflected by different enzymatic mechanisms. The broad substrate specificity is revealed by the heterogeneity of physiological substrates of plant and animal QCs, including cytokines, matrix proteins and pathogenesis-related proteins. Moreover, recent evidence also suggests human QC as a catalyst of pGlu formation at the N-terminus of amyloid peptides, which contribute to Alzheimer's disease. Obviously, owing to its biophysical properties, the function of pGlu in plant and animal proteins is very similar in terms of stabilizing or mediating protein and peptide structure. It is possible that the requirement for catalysis of pGlu formation under physiological conditions may have triggered separate evolution of QCs in plants and animals.