Accelerated Evolution in the Protein-coding Region of Galectin cDNAs, Congerin I and Congerin II, from Skin Mucus of Conger Eel (Conger myriaster)

Abstract

Two cDNAs encoding galectins named congerins I and II from the skin mucus of conger eel (Conger myriaster) were isolated and sequenced. Comparison of the nucleotide sequences of congerins I and II showed that the sequence similarities of the 5' and 3' untranslated regions (86 and 88%, respectively) were much higher than those of the protein-coding region (73%). The numbers of nucleotide substitutions per site (KN) for the untranslated regions are smaller than the numbers of nucleotide substitutions per synonymous site (KS) for the protein coding region. Furthermore, nonsynonymous nucleotide substitutions have accelerated more frequently than synonymous nucleotide substitutions in the protein coding region (KA/KS = 2.57). These results suggest that accelerated substitutions have occurred in the protein-coding regions of galectin genes to generate diverse galectins with different molecular properties. Northern blot analysis showed that both congerins were expressed not only in the skin tissues but also in the stomach of conger eel.

Allosteric Regulation of the Carbohydrate-binding Ability of a Novel Conger Eel Galectin by d-Mannoside

“…S1B). In general, Con-P was expressed in almost all of the various tissues analyzed except for spleen; however, expression of Con I and Con II was restricted to the skin and upper digestive tract as reported previously (4,24). In some specimens, Con-P was the only congerin isotype expressed in the peritoneal cells and was also transcribed in encapsulated bodies in the abdominal cavity.…”

“…The conger eel (Conger myriaster) contains two prototype galectins, congerins I and II (Con I and II), that are found in the skin mucus and frontier organs that delineate the body from the outer environment, such as the epidermal club cells of the skin, wall of the oral cavity, pharynx, esophagus, and gills (3,4). Con I and II are prototype galectins, composed of subunits containing 135 and 136 amino acids, respectively, and display 48% amino acid sequence identity (4 -6).…”

“…Con I and II are prototype galectins, composed of subunits containing 135 and 136 amino acids, respectively, and display 48% amino acid sequence identity (4 -6). Previous studies of Con I and Con II based on molecular evolutionary and x-ray crystallography analyses revealed that these proteins have evolved via accelerated substitutions under natural selection pressure from ancestors (4,(7)(8)(9)(10)(11)(12)(13). As a result, Con I has acquired a new strand-swap fold, which stabilizes the dimer structure that is essential for pathogen-coagulating activity.…”

An Overview of the Immunological Defenses in Fish Skin

“…In the case of congerins I and II, they can recognize some marine bacteria such as Vibrio anguillarum [198]. Investigation of their localization in fish tissues suggested that they are expressed not only in skin but also in the upper digestive tract and gill filament [198,199]. Eel has an additional lectin, AJL-2, which has a highly conserved sequence of C-type lectins, but displays Ca2q-independent activity.…”

Cloning and characterisation of tandem-repeat type galectin in rainbow trout (Oncorhynchus mykiss)

“…In fish, conger eel and electric eel have the proto-type galectin homologous protein and/or gene (Paroutaud et al, 1987;Muramoto & Kamiya, 1992;Ogawa et al, 1999). Eel proto-type galectin was isolated from the electric organ of Electrophorus electricus and found to have a prophylactic and therapeutic action on the experimental autoimmune myasthenia gravis in rabbit.…”