Phylogenetic and crystallographic analysis of Nostoc phycocyanin having blue-shifted spectral properties.

ABSTRACT: The distinct sequence feature and spectral blue-shift (~10?nm) of phycocyanin, isolated from Nostoc sp. R76DM (N-PC), were investigated by phylogenetic and crystallographic analyses. Twelve conserved substitutions in N-PC sequence were found distributed unequally among ?- and ?-subunit (3 in ?- and 9 in ?-subunit). The phylogenetic analysis suggested that molecular evolution of ?- and ?-subunit of Nostoc-phycocyanin is faster than evolution of Nostoc-species. The divergence events seem to have occurred more frequently in ?-subunit, compared to ?-subunit (relative divergence, 7.38 for ?-subunit and 9.66 for ?-subunit). Crystal structure of N-PC was solved at 2.35?Å resolution to reasonable R-factors (Rwork/RFree?=?0.199/0.248). Substitutions congregate near interface of two ??-monomer in N-PC trimer and are of compensatory nature. Six of the substitutions in ?-subunit may be involved in maintaining topology of ?-subunit, one in inter-monomer interaction and one in interaction with linker-protein. The ?153Cys-attached chromophore adopts high-energy conformational state resulting due to reduced coplanarity of B- and C-pyrrole rings. Distortion in chromophore conformation can result in blue-shift in N-PC spectral properties. N-PC showed significant in-vitro and in-vivo antioxidant activity comparable with other phycocyanin. Since Nostoc-species constitute a distinct phylogenetic clade, the present structure would provide a better template to build a model for phycocyanins of these species.

SUBMITTER: Sonani RR 

PROVIDER: S-EPMC6614406 | biostudies-literature | 2019 Jul

REPOSITORIES: biostudies-literature