RESUMO
BACKGROUND: Mutations in the human polycystic kidney disease-1 (hPKD1) gene result in ~85% of cases of autosomal dominant polycystic kidney disease, the most frequent human monogenic disease. PKD1 proteins are large multidomain proteins involved in a variety of signal transduction mechanisms. Obtaining more information about members of the PKD1 family will help to clarify their functions. Humans have five hPKD1 proteins, whereas sea urchins have 10. The PKD1 proteins of the sea urchin, Strongylocentrotus purpuratus, are referred to as the Receptor for Egg Jelly, or SpREJ proteins. The SpREJ proteins form a subfamily within the PKD1 family. They frequently contain C-type lectin domains, PKD repeats, a REJ domain, a GPS domain, a PLAT/LH2 domain, 1-11 transmembrane segments and a C-terminal coiled-coil domain. RESULTS: The 10 full-length SpREJ cDNA sequences were determined. The secondary structures of their deduced proteins were predicted and compared to the five human hPKD1 proteins. The genomic structures of the 10 SpREJs show low similarity to each other. All 10 SpREJs are transcribed in either embryos or adult tissues. SpREJs show distinct patterns of expression during embryogenesis. Adult tissues show tissue-specific patterns of SpREJ expression. CONCLUSION: Possession of a REJ domain of about 600 residues defines this family. Except for SpREJ1 and 3, that are thought to be associated with the sperm acrosome reaction, the functions of the other SpREJ proteins remain unknown. The sea urchin genome is one-fourth the size of the human genome, but sea urchins have 10 SpREJ proteins, whereas humans have five. Determination of the tissue specific function of each of these proteins will be of interest to those studying echinoderm development. Sea urchins are basal deuterostomes, the line of evolution leading to the vertebrates. The study of individual PKD1 proteins will increase our knowledge of the importance of this gene family.
Assuntos
Proteínas do Ovo/genética , Regulação da Expressão Gênica , Mutação , Canais de Cátion TRPP , Animais , Clonagem Molecular , DNA Complementar/metabolismo , Proteínas do Ovo/química , Humanos , Modelos Genéticos , Família Multigênica , Estrutura Secundária de Proteína , Estrutura Terciária de Proteína , Ouriços-do-Mar , Análise de Sequência de DNA , Distribuição TecidualRESUMO
A wealth of evidence shows that protein-carbohydrate recognition mediates the steps of gamete interaction during fertilization. Carbohydrate-recognition domains (CRDs) comprise a large family of ancient protein modules of approximately 120 amino acids, having the same protein fold, that bind terminal sugar residues on glycoproteins and polysaccharides. Sea urchin sperm express three suREJ (sea urchin receptor for egg jelly) proteins on their plasma membranes. suREJ1 has two CRDs, whereas suREJ2 and suREJ3 both have one CRD. suREJ1 binds the fucose sulfate polymer (FSP) of egg jelly to induce the sperm acrosome reaction. The structure of FSP is species specific. Therefore, the suREJ1 CRDs could encode molecular recognition between sperm and egg underlying the species-specific induction of the acrosome reaction. The functions of suREJ2 and suREJ3 have not been explored, but suREJ3 is exclusively localized on the plasma membrane over the sperm acrosomal vesicle and is physically associated with sea urchin polycystin-2, a known cation channel. An evolutionary analysis of these four CRDs was performed for six sea urchin species. Phylogenetic analysis shows that these CRDs were already differentiated in the common ancestor of these six sea urchins. The CRD phylogeny agrees with previous work on these species based on one nuclear gene and several mitochondrial genes. Maximum likelihood shows that positive selection acts on these four CRDs. Threading the suREJ CRDs onto the prototypic CRD crystal structure shows that many of the sites under positive selection are on extended loops, which are involved in saccharide binding. This is the first demonstration of positive selection in CRDs and is another example of positive selection acting on the evolution of gamete-recognition proteins.
Assuntos
Evolução Molecular , Receptores de Superfície Celular/genética , Ouriços-do-Mar/genética , Seleção Genética , Interações Espermatozoide-Óvulo/genética , Animais , Feminino , Fucose/análogos & derivados , Fucose/genética , Fucose/metabolismo , Masculino , Ligação Proteica/genética , Ligação Proteica/fisiologia , Estrutura Terciária de Proteína/genética , Estrutura Terciária de Proteína/fisiologia , Receptores de Superfície Celular/metabolismo , Ouriços-do-Mar/metabolismo , Ácidos Sulfúricos/metabolismoRESUMO
Abalone (gastropod mollusks) express a protein, abMpeg1, which is a homolog of two mammalian proteins that share homology with mammalian perforin, a cytolytic and immune-regulatory protein of lymphocytes. One of the mammalian proteins, Mpeg1, is expressed in mature macrophage and prion-infected mouse brains, while the other, Epcs50, is expressed in ectoplacental cone cells of the invading placenta. Although the functions of these three proteins remain unknown, their structural similarity to mammalian perforin suggests that they may be involved in cell killing, the inflammatory response or tissue invasion. Consistent with these proposed functions, the Mpeg1 gene family shows the signature of positive Darwinian selection (adaptive evolution). The perforin-homology domain of abMpeg1 contains the cytolytic "helix-turn-helix" domain of perforin, supporting the idea that abMpeg1 is a cytolytic protein of the abalone innate immune system. The alpha-helices of abMpeg1 are amphipathic as are those of perforin. The conservation among abMpeg1, mammalian Mpeg1, and Epcs50 shows that Mpeg1 proteins represent a novel, ancient protein family of probable immunological function.
