Comparative study of 7s globulin from corylus avellana and solanum lycopersicum revealed importance of salicylic acid and cu-Binding loop in modulating their function.
The plant seed proteins referred to as vicilins belong to a structurally common
superfamily. While some of them are reported to exhibit superoxide dismutase
activity, vicilins from other sources do not possess this activity. Vicilin from
Corylus avellana (HZ.1) and Solanum lycopersicum (SL80.1) were purified and
subjected to structure-function analysis. The superoxide dismutase activity
assays were performed to understand the functional differences between them.
While SL80.1 has the superoxide dismutase activity, HZ.1 was enzymatically
inactive. Crystal structure followed by mass spectrometry analysis of both the
proteins revealed that while SL80.1 has bound salicylic acid, HZ.1 does not.
Comparison of C-terminal binding pocket of both the structures revealed that a
point mutation at residue 321 in HZ.1 (Gly→Cys) leads to obstruction in
binding of salicylic acid in the pocket. Similarly, copper-binding loop of HZ.1
was reportedly found to be intact and shorter than the loops reported in SL80.1.
The copper-binding loop of SL80.1 is rich in polar residues and the absence of
these residues in HZ.1 copper-binding loop possibly indicates deficiency in
channeling of oxygen radicals to the active center of the enzyme. Difference in
the enzymatic activity of vicilin from two evolutionarily distinct sources is
due to mutations in its co-factor binding pocket and copper-binding loop.
