Molecular characterization and tissue distribution of 23 kDa membrane protein encoding gene from Schistosoma mekongi

Abstract

The objectives of this study are: (1) To clone and characterized 23 kDa membrane protein gene from S. mekongi. (2) To predict the potential immunogenic epitope of 23 kDa membrane protein from S. mekongi. (3) To study the distribution of Smek23 in parasite tissues. Schistosoma mekongi is one important human parasitic which causes liver damage in South-east Asia. 23 kDa protein is an integral membrane protein of the blood fluke genus Schistosoma and its expressed in all parasite stages. The cDNA encoding Smek23 of adult S. mekongi was cloned and sequenced. The nucleotide sequence of Smek23 was 686 bp in length. The nucleotide sequence of Smek23 showed an open reading frame encoding 23 kDa integral membrane protein containing 218 amino acids. The expected molecular weight of Smek23 determined from its constituent amino acids is 23.62 kDa. Smek23 has four transmembrane domains (TM). The localization of Smek23 demonstrates that the molecule is localized to tegument membrane compartments. The Smek23 amino acid sequences showed the highest degree of identity with the S. turkestanicum 23 kDa. The identity of Smek23 amino acid sequences with other schistosome species (S. mansoni, S. japonicum and S. haematobium showed at 87.6-89.9% respectively. Phylogenetic analysis in this study revealed that Smek23 exhibited a distant evolutionary relationship from the Tetraspanin of mammalian host species (CD63, CD81). The low degree of conservation observed from amino acid sequences of mammalian hosts could reveal its applicability for use as the vaccine candidate against the schistosome infection which may not interfere with the hosts’ Tetraspanin molecule during the vaccination. Three candidate B cell immunogenic epitopes were predicted by four programs (Hopp and Woods, Welling, Parker, and B-EpiPred). These regions were 111-KIDA-114, 125-DHP-127, and 150-PNDYKGSVPDSCKEGQVPYT-169. All of these three regions were located in extracellular domain 2 (EXT 2), which is a large hydrophilic domain (LHD) of Smek23 molecule. The predicted epitopes provide promising vaccine candidates and could be tested by a wet laboratory as a targeted vaccine against S. mekongi infection.

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