Authors: ZAHOOR QADIR SAMRA, MUHAMMAD AMIN ATHAR
Abstract: The \beta-mannosidase (MANB) enzyme is involved in removing mannose residue from the nonreducing end, and its impaired activity leads to \beta-mannosidosis. MANB amino acid sequences of humans, other mammals, plants, fungi, and bacteria were compared to determine their similarities, differences, and predicted 3D structures. Our cloned MANB DNA sequence showed a 99% similarity to a previously reported human MANB DNA sequence but 16 nucleotide differences were observed, showing the polymorphic nature of the enzyme. The 9 changed codons coded the different amino acids Ile, Lys, Ile, Thr, Arg, Leu, Leu, Gly, and Asp, while 7 changed codons coded the same amino acids, Ile, Arg, Gln, Val, Ile, Pro, and Val. The amino acid sequence comparison of human MANB with bovine, goat, and mouse MANB showed a nearly 75% similarity, while 10%-13%, 17%-18%, and 9%-23% similarities were observed with plant, fungi, and bacteria MANB, respectively. The catalytic nucleophilic and proton donor sites were conserved in the /beta-mannosidase of mammals, plants, fungi, and bacteria, except L. esculentum, and the nucleophilic site of P. furiosus was also changed. The catalytic sites of MANB indicated that it follows a dyad catalytic mechanism. Additionally, 2 common putative glycosylation sites at N-residues 35 and 77 were conserved. The 3D structure prediction indicated differences in the α-helix loop, while the \beta-pleated sheets were nearly the same. The comparison showed that the MANB enzyme is polymorphic in nature with conserved catalytic sites and has an evolutionary relationship among different species. The 3D structure comparison of MANB will be helpful to understand the disease process of \beta-mannosidosis.
Keywords: \beta-Mannosidase, DNA sequence, amino acid comparison, computational analysis
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