RESUMEN
The primary structure of catfish (Silurus asotus) egg lectin (SAL) was determined. SAL cDNA contained 1448-bp nucleotides and 308 amino acid residues, deduced from open reading frame. The SAL mature protein composed of 285-amino acid residues was followed by a predicted signal sequence having 23 residues. The mRNA of SAL was found to be expressed in eggs, but not in liver. SAL is composed of three tandem repeat domain structures divided into exactly 95 amino acid residues each, and all cysteine positions of each domain were completely conserved. Sequence homologies between the three domains, termed D1 (1-95), D2 (96-190) and D3 (191-285), were as follows; D1-D2, 28%; D2-D3, 33%; D1-D3, 43%. Two conserved peptide motifs, -(AN)YGR(TD)S(T)XCS(TGR)P- and -DPCX(G)T(Y)KY(L)-, appear to exist at the N- and C-terminal regions of each domain, respectively. The kinetic parameters of SAL obtained by measuring surface plasmon resonance were as follows: K(a) (M(-1)) for neohesperidosyl-BSA, 7. 1 x 10(6); for melibiosyl-BSA, 4.9 x 10(6); and for lactosyl-BSA, 5. 2 x 10(5). These results show that RBLs including SAL comprise a family of alpha-galactosyl binding lectins having characteristic tandem repeat domain structures.
Asunto(s)
Bagres/genética , Proteínas de Peces , Lectinas/genética , Secuencia de Aminoácidos , Animales , Secuencia de Bases , Bagres/embriología , ADN Complementario/química , Glicoproteínas/química , Lectinas/biosíntesis , Lectinas/química , Espectrometría de Masas , Datos de Secuencia Molecular , ARN Mensajero/biosíntesis , Alineación de Secuencia , Homología de Secuencia de Aminoácido , Relación Estructura-Actividad , Secuencias Repetidas en TándemAsunto(s)
Glicósido Hidrolasas , Sitios de Unión , Glucosa , Cinética , Maltosa , Matemática , Modelos Biológicos , Oligosacáridos , Polisacáridos , Unión Proteica , Conformación Proteica , Rhizopus/enzimologíaRESUMEN
Physarumin, a carbohydrate-binding protein (hemagglutinin or lectin), was isolated from the plasmodium of Physarum polycephalum. Physarumin agglutinated not only several species of erythrocytes but also tumor cells such as AH109A ascites hepatoma cells, sarcoma 180 ascites cells and mouse leukemia P388 cell lines. Physarumin had tumor cell growth-inhibitory activity, and induced the apoptosis of P388 cell lines. Physarumin-induced apoptosis required binding to a 68 kDa counter-receptor on the P388 cell surface. Since the agglutinating and antiproliferative activities of physarumin were inhibited by asialofetuin and thyroglobulin, respectively, it is suggested that physarumin reacts with the galactose moiety of carbohydrate chains of physarumin receptor.