The myoclonus epilepsy associated with ragged-red fibers (MERRF) is a mitochondrial encephalomyopathic disease caused due to the lack of hypermodified nucleoside 5-taurinomethyl-2-thiouridine at 'wobble' 34th position in the anticodon loop of human mitochondrial tRNA Lys . Understanding the structural significance of sm 5 s 2 U might be helpful to get more information about the MERRF disease in detail at the atomic level. Hence, conformational preferences of hypermodified nucleoside 5-taurinomethyl-2-thiouridine 5 0 -monophosphate, 'p-sm 5 s 2 U,' have been studied using semiempirical quantum chemical RM1 method. Full geometry optimization using ab initio molecular orbital HF-SCF (6-31G**) and DFT (B3LYP/6-31G**) methods has also been used to compare the salient features. The RM1 preferred most stable conformation of 'p-sm 5 s 2 U' has been stabilized by hydrogen bonding interactions between O(11a)…HN (8), O1P (34) … HN(8), O1P (34) …HC(10), O4 0 (34) …HC(6), S(2)…HC1 0 (34), O5 0 (34) …HC(6), and O(4)…HC (7). Another conformational study of 5-taurinomethyl-2-thiouridine side chain in the presence of anticodon loop bases of human mitochondrial tRNA Lys showed similar conformation as found in RM1 preferred most stable conformation of 'p-sm 5 s 2 U.' The glycosyl torsion angle of sm 5 s 2 U retains 'anti' conformation. Similarly, MD simulation results are also found in accordance with RM1 preferred stable structure. The solvent-accessible surface area calculations revealed surface accessibility of sm 5 s 2 U in human mt tRNA Lys anticodon loop. The MEPs calculations of codon-anticodon models of sm 5 s 2 U (34) :G 3 and sm 5 s 2 U (34) :A 3 showed unique potential tunnels between the hydrogen bond donor and acceptor atoms. These results might be useful to understand the exact role of sm 5 s 2 U (34) to recognize AAG/ AAA codons and to design new strategies to prevent mitochondrial disease, MERRF.