Co-Evolution of Opioid and Adrenergic Ligands and Receptors: Shared, Complementary Modules Explain Evolution of Functional Interactions and Suggest Novel Engineering Possibilities

Cross-talk between opioid and adrenergic receptors is well-characterized and involves second messenger systems, the formation of receptor heterodimers, and the presence of extracellular allosteric binding regions for the complementary ligand; however, the evolutionary origins of these interactions have not been investigated. We propose that opioid and adrenergic ligands and receptors co-evolved from a common set of modular precursors so that they share binding functions. We demonstrate the plausibility of this hypothesis through a review of experimental evidence for molecularly complementary modules and report unexpected homologies between the two receptor types. Briefly, opioids form homodimers also bind adrenergic compounds; opioids bind to conserved extracellular regions of adrenergic receptors while adrenergic compounds bind to conserved extracellular regions of opioid receptors; opioid-like modules appear in both sets of receptors within key ligand-binding regions. Transmembrane regions associated with homodimerization of each class of receptors are also highly conserved across receptor types and implicated in heterodimerization. This conservation of multiple functional modules suggests opioid–adrenergic ligand and receptor co-evolution and provides mechanisms for explaining the evolution of their crosstalk. These modules also suggest the structure of a primordial receptor, providing clues for engineering receptor functions.

Mutual Enhancement of Opioid and Adrenergic Receptors by Combinations of Opioids and Adrenergic Ligands Is Reflected in Molecular Complementarity of Ligands: Drug Development Possibilities

Crosstalk between opioid and adrenergic receptors is well characterized and due to interactions between second messenger systems, formation of receptor heterodimers, and extracellular allosteric binding regions. Both classes of receptors bind both sets of ligands. We propose here that receptor crosstalk may be mirrored in ligand complementarity. We demonstrate that opioids bind to adrenergic compounds with micromolar affinities. Additionally, adrenergic compounds bind with micromolar affinities to extracellular loops of opioid receptors while opioids bind to extracellular loops of adrenergic receptors. Thus, each compound type can bind to the complementary receptor, enhancing the activity of the other compound type through an allosteric mechanism. Screening for ligand complementarity may permit the identification of other mutually-enhancing sets of compounds as well as the design of novel combination drugs or tethered compounds with improved duration and specificity of action.

Rapid Non-Enzymatic Glycation of the Insulin Receptor under Hyperglycemic Conditions Inhibits Insulin Binding In Vitro: Implications for Insulin Resistance

The causes of insulin resistance are not well-understood in either type 1 or type 2 diabetes. Insulin (INS) is known to undergo rapid non-enzymatic covalent conjugation to glucose or other sugars (glycation). Because the insulin receptor (IR) has INS-like regions associated with both glucose and INS binding, we hypothesize that hyperglycemic conditions may rapidly glycate the IR, chronically interfering with INS binding. IR peptides were synthesized spanning IR- associated INS-binding regions. Glycation rates of peptides under hyperglycemic conditions were followed over six days using matrix assisted laser desorption/ionization-time of flight (MALDI-TOF) mass spectrometry. INS conjugated to horse-radish peroxidase was used to determine INS binding to IR peptides in glycated and non-glycated forms. Several IR peptides were glycated up to 14% within days of exposure to 20-60 mM glucose. Rates of IR-peptide glycation were comparable to those of insulin. Glycation of four IR peptides significantly inhibits INS binding to them. Glycation of intact IR also decreases INS binding by about a third, although it was not possible to confirm the glycation sites on the intact IR. Glycation of the IR may therefore provide a mechanism by which INS resistance develops in diabetes. Demonstration of glycation of intact IR in vivo is needed.

tRNA evolution from the proto-tRNA minihelix world

Multiple models have been advanced for the evolution of cloverleaf tRNA. Here, the conserved archaeal tRNA core (75-nt) is posited to have evolved from ligation of three proto-tRNA minihelices (31-nt) and two-symmetrical 9-nt deletions within joined acceptor stems (93 – 18 = 75-nt). The primary evidence for this conclusion is that the 5-nt stem 7-nt anticodon loop and the 5-nt stem 7-nt T loop are structurally homologous and related by coding sequence. We posit that the D loop was generated from a third minihelix (31-nt) in which the stem and loop became rearranged after 9-nt acceptor stem deletions and cloverleaf folding. The most 3´-5-nt segment of the D loop and the 5-nt V loop are apparent remnants of the joined acceptor stems (14 – 9 = 5-nt). Before refolding in the tRNA cloverleaf, we posit that the 3′-5-nt segment of the D loop and the 5-nt V loop were paired, and, in the tRNA cloverleaf, frequent pairing of positions 29 (D loop) and 47 (V loop) remains (numbered on a 75-nt tRNA cloverleaf core). Amazingly, after >3.5 billion years of evolutionary pressure on the tRNA cloverleaf structure, a model can be constructed that convincingly describes the genesis of 75/75-nt conserved archaeal tRNA core positions. Judging from the tRNA structure, cloverleaf tRNA appears to represent at least a second-generation scheme (and possibly a third-generation scheme) that replaced a robust 31-nt minihelix protein-coding system, evidence for which is preserved in the cloverleaf structure. Understanding tRNA evolution provides insights into ribosome and rRNA evolution.

Efeito do treinamento aeróbio nos níveis de homocisteína em indivíduos diabéticos do tipo 2

INTRODUÇÃO: Os programas de treinamento aeróbio têm demonstrado bons resultados no controle das variáveis de risco cardiovascular em indivíduos diabéticos; no entanto, os efeitos nos níveis de homocisteína não estão claros. Objetivo: Analisar os efeitos do treinamento aeróbio nos níveis plasmáticos de homocisteína e fatores de risco cardiovascular em indivíduos diabéticos do tipo 2.MÉTODOS: Participaram do estudo 15 mulheres com diabetes do tipo 2 e média de idade 68,86 ± 11,2 anos. Todos os indivíduos da amostra foram submetidos a um teste de avaliação do consumo máximo de oxigénio (VO2máx) seguindo o protocolo de Bruce, avaliação da pressão arterial e avaliação antropométrica. Foi também efetuada uma coleta de 10 ml de sangue (veia antecubital) em jejum de no mínimo 12 horas. O plasma foi separado e processado para posterior análise da concentração de homocisteína (mmol/l), colesterol total (mg/dl), lipoproteína de muito baixa densidade (VLDL) (mg/dl), lipoproteína de baixa densidade (LDL) (mg/dl), lipoproteína de alta densidade (HDL) (mg/dl), triglicérides (mg/dl) e glicemia (mg/dl). Os testes foram feitos antes e após 16 semanas de treinamento aeróbio. O programa foi realizado com 2 sessões de treinamento não consecutivas por semana, com intensidade compreendida entre 60% e 70% da frequência cardíaca máxima e duração de 75 minutos por sessão.RESULTADOS: Os resultados observados revelam que o programa de exercício físico induziu uma diminuição não significativa da concentração plasmática de homocisteína. Foram ainda identificadas melhorias do perfil lipídico e do Consumo Máximo de Oxigênio (VO2máx), diminuição da glicemia, da pressão arterial diastólica, do percentual de gordura e massa gorda.CONCLUSÃO: Conclui-se que o programa de treinamento aeróbio reduziu o risco cardiovascular em indivíduos diabéticos do tipo 2, embora a alteração da homocisteína não tenha sido significativa.