Affiliations: Department of Biotechnology, School of Biotechnology
and Genetic Engineering, Bharathiar University, Coimbatore, Tamilnadu, 641046,
India
Abstract: Although butyrylcholinesterase (BChE) is ubiquitous in the human
system, its physiological function has often been questioned. Yet BChE has been
the subject of active research since its discovery six decades ago. From an
evolutionary view point, its stabilized existence even in absence of
physiological function spared it from extinction. Herein, we present results on
the amino acid residues essential for its stability using CUPSAT server. Out of
the 523 amino acids analyzed, 168 were identified to be vital for stability of
the protein, and further categorized into three classes. The first class has 82
sites wherein any amino acid substitution results in instability. The second
class has 52 sites where on one amino acid substitution alone stability is
observed, while the third class has 34 sites where even on two different
substitutions, stability is maintained. These sites are distributed throughout
the different categories of protein secondary structure, with the order of
priority: random coils, α-helices and β-strands. Multiple sequence alignment of BChE showed that most of
these residues (85.1%) are within the conserved region, while the few that
are not at the conserved region are proposed to be unique residues (14.9%)
to the protein which do not show identity with other known homologs. Moreover,
majority of the amino acid residues in the functional regions of human BChE do
not show instability upon point mutation, indicative of the residue-wise
separation for stability and function. Specifically, the active site S198 on
mutation does not show instability, while L318P is highly unstable. In
addition, S53, G212 and W430 are not involved in its stability and in fact the
protein is stable even with all other 19 substitutions. In conclusion, this
study bodes well as a forerunner for mutation and protein engineering studies
of BChE.
