Crystal Structure of Imaginal Disc Growth Factor-2

Imaginal disc growth factor-2 (IDGF-2) is a member of a recently described family of Drosophila melanogaster-soluble polypeptide growth factors that promote cell proliferation in imaginal discs. Although their precise mode of action has not been established, IDGFs cooperate with insulin in stimulating the growth of imaginal disc cells. We report the crystal structure of IDGF-2 at 1.3-A resolution. The structure shows the classical (betaalpha)(8) barrel-fold of family 18 glycosyl hydrolases, with an insertion of an alpha + beta domain similar to that of Serratia marcescens chitinases A and B. However, amino acid substitutions in the consensus catalytic sequence of chitinases give IDGF-2 a less negatively charged environment in its putative ligand-binding site and preclude the nucleophilic attack mechanism of chitin hydrolysis. Particularly important is the replacement of Glu by Gln at position 132, which has been shown to abolish enzymatic activity in chitinases. Nevertheless, a modest conservation of residues that participate in oligosaccharide recognition suggests that IDGF-2 could bind carbohydrates, assuming several conformational changes to open the partially occluded binding site. Thus, IDGFs may have evolved from chitinases to acquire new functions as growth factors, interacting with cell surface glycoproteins implicated in growth-promoting processes, such as the Drosophila insulin receptor.Fil: Varela, Paloma F.. University of Maryland; Estados UnidosFil: Llera, Andrea Sabina. University of Maryland; Estados Unidos. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Bioquímicas de Buenos Aires. Fundación Instituto Leloir. Instituto de Investigaciones Bioquímicas de Buenos Aires; ArgentinaFil: Mariuzza, Roy A.. University of Maryland; Estados UnidosFil: Tormo, José. Universidad Autónoma de Madrid; Españ

Cis - trans interactions of cell surface receptors: biological roles and structural basis

Cell surface receptors bind ligands expressed on other cells (in trans) in order to communicate with neighboring cells. However, an increasing number of cell surface receptors are found to also interact with ligands expressed on the same cell (in cis). These observations raise questions regarding the biological role of such cis interactions. Specifically, it is important to know whether cis and trans binding have distinct functional effects and, if so, how a single cell discriminates between interactions in cis versus trans. Further, what are the structural features that allow certain cell surface receptors to engage ligand both on the same as well as on an apposed cell membrane? Here, we summarize known examples of receptors that display cis-trans binding and discuss the emerging diversity of biological roles played by these unconventional two-way interactions, along with their structural basi

Structural Basis for Recognition of Cellular and Viral Ligands by NK Cell Receptors

Natural killer (NK) cells are key components of innate immune responses to tumors and viral infections. NK cell function is regulated by NK cell receptors that recognize both cellular and viral ligands, including major histocompatibility complex (MHC), MHC-like, and non-MHC molecules. These receptors include Ly49s, killer immunoglobulin-like receptors, leukocyte immunoglobulin-like receptors, and NKG2A/CD94, which bind MHC class I (MHC-I) molecules, and NKG2D, which binds MHC-I paralogs such as the stress-induced proteins MICA and ULBP. In addition, certain viruses have evolved MHC-like immunoevasins, such as UL18 and m157 from cytomegalovirus, that act as decoy ligands for NK receptors. A growing number of NK receptor–ligand interaction pairs involving non-MHC molecules have also been identified, including NKp30–B7-H6, killer cell lectin-like receptor G1–cadherin, and NKp80–AICL. Here, we describe crystal structures determined to date of NK cell receptors bound to MHC, MHC-related, and non-MHC ligands. Collectively, these structures reveal the diverse solutions that NK receptors have developed to recognize these molecules, thereby enabling the regulation of NK cytolytic activity by both host and viral ligands

Selection of the lamprey VLRC antigen receptor repertoire

The alternative adaptive immune system of jawless vertebrates is based on different isotypes of variable lymphocyte receptors (VLRs) that are composed of leucine-rich repeats (LRRs) and expressed by distinct B- and T-like lymphocyte lineages. VLRB is expressed by B-like cells, whereas VLRA and VLRC are expressed by two T-like lineages that develop in the thymoid, a thymus-like structure in lamprey larvae. In each case, stepwise combinatorial insertions of different types of short donor LRR cassettes into incomplete germ-line genes are required to generate functional VLR gene assemblies. It is unknown, however, whether the diverse repertoires of VLRs that are expressed by peripheral blood lymphocytes are shaped by selection after their assembly. Here, we identify signatures of selection in the peripheral repertoire of VLRC antigen receptors that are clonally expressed by one of the T-like cell types in lampreys. Selection strongly favors VLRC molecules containing four internal variable leucine-rich repeat (LRRV) modules, although VLRC assemblies encoding five internal modules are initially equally frequent. In addition to the length selection, VLRC molecules in VLRC+ peripheral lymphocytes exhibit a distinct pattern of high entropy sites in the N-terminal LRR1 module, which is inserted next to the germ-line–encoded LRRNT module. This is evident in comparisons to VLRC gene assemblies found in the thymoid and to VLRC gene assemblies found in some VLRA+ cells. Our findings are the first indication to our knowledge that selection operates on a VLR repertoire and provide a framework to establish the mechanism by which this selection occurs during development of the VLRC+ lymphocyte lineage

The Interaction with H-2Dd in cis is Associated with a Conformational Change in the Ly49A NK Cell Receptor

Mouse natural killer (NK) cells express Ly49 family receptors that recognize major histocompatibility complex class I (MHC-I) molecules. By interacting with MHC-I molecules expressed on other cells (in trans), inhibitory Ly49 receptors prevent the NK cell-mediated killing of normal cells. In addition, some Ly49 receptors have the unusual property to also interact with MHC-I molecules expressed by the NK cell itself (in cis). cis Binding sequesters a significant fraction of the NK cells’ Ly49 receptors, reducing the number of receptors available for trans binding. This lowers the threshold at which NK cell activation exceeds inhibition rendering NK cells more sensitive. It is unclear how Ly49 receptors can bind MHC-I in trans and in cis using the same binding site. We have proposed that this is mediated by two distinct conformations of Ly49 receptors. Here we have tested this model by inferring the distance between the ligand-binding domain of Ly49A and the cell membrane using fluorescence resonance energy transfer (FRET). Consistent with the concept, reducing the distance between the ligand-binding domain of Ly49A and the cell membrane, by shortening the Ly49A stalk, resulted in a substantially increased FRET. The co-expression of cognate MHC-I ligand reduced FRET derived from Ly49A variants with a shortened stalk, indicating that cis association alters FRET. Indeed, FRET improved when cis complexes were disrupted using acid-mediated destruction of MHC-I complexes. These data provide direct evidence that the interaction with MHC-I in cis is associated with a conformational change in the Ly49A receptor on the surface of live cells. The novel FRET based approach may be generally applicable to study conformational changes in cell surface receptors

Associação do consumo alimentar e estado nutricional de praticantes de musculação

Thus, the objective of this study was to evaluate the food consumption and nutritional status of bodybuilding practitioners. Materials and Methods: Sociodemographic, food consumption (two recalls) and anthropometric (weight, height and skin folds) data were collected. The averages of the recalls were compared with the references of the Dietary References Intakes (NASEN, 2017; 2019) and the Brazilian Society of Exercise and Sports Medicine (SBME, 2009). The Body Mass Index (BMI) and % of body fat were calculated. Results: 71 bodybuilders participated in the study, most of them in eutrophic state (63.4%), followed by overweight/obesity (33.8%). The average consumption of carbohydrates was significantly lower than the recommendations, 41.7% of the total energy value (VET), while the average consumption of lipids was significantly higher, 35.8% of the VET. The consumption of vitamin D, potassium and fiber was significantly lower than the recommendations in both genders, in contrast, the consumption of sodium was significantly higher. Iron consumption was significantly above the recommendations among men and significantly lower among women. Conclusion: It was observed an inadequate consumption of carbohydrates, proteins, lipids, vitamin D, potassium and fibers by bodybuilders in relation to the recommendations, requiring a greater role of the nutritionist in the gyms in order to promote the adequacy of food consumption.O objetivo deste estudo foi avaliar o consumo alimentar e estado nutricional de praticantes de musculação. Materiais e Métodos: Foram coletados dados sociodemográficos, de consumo alimentar (dois recordatórios) e antropométricos (peso, altura e dobras cutâneas). As médias dos recordatórios foram comparadas com as referências da Dietary References Intakes (NASEN, 2017; 2019) e da Sociedade Brasileira de Medicina do Exercício e do Esporte (SBME, 2009). Foi calculado o Ãndice de Massa Corporal (IMC) e % de gordura corporal. Resultados: Participaram do estudo 71 praticantes de musculação, a maioria em estado de eutrofia (63,4%), seguido de sobrepeso/obesidade (33,8%). A média do consumo de carboidratos foi significativamente inferior às recomendações, 41,7% do valor energético total (VET), enquanto, o consumo de lipídeos foi significativamente superior, 35,8% do VET. O consumo de vitamina D, potássio e fibras foi significativamente inferior às recomendações em ambos os gêneros, em contrapartida, o consumo de sódio foi significativamente superior. O consumo de ferro foi significativamente acima das recomendações entre os homens e significativamente inferior entre as mulheres. Conclusão: Foi observado consumo inadequado de carboidratos, proteínas, lipídios, vitamina D, potássio e fibras por praticantes de musculação em relação às recomendações, sendo necessário uma maior atuação do nutricionista nas academias a fim de promover a adequação do consumo alimentar