Archaeal Sm-like proteins belong to the large LSm family,
which is characterized by the ability to adopt Sm fold. It is comprised of a
5-stranded β-sheet
and an N-terminal α-helix. Despite the fact that they are structurally
conserved, functions of the protein from archaea, bacteria and eukarya are
dissimilar.
Eukaryotes contain at least 18 different Lsm proteins
involved in mRNA splicing, telomere maintenance and mRNA degradation. In bacteria there is a single bacterial Lsm protein
called Hfq. It acts as an RNA
chaperone facilitating interaction between regulatory RNA and mRNA. Archaeal
genomes encode one or two Sm-like proteins belonging to two subfamilies SmAP1
and SmAP2. Homology between SmAP1 protein sequences of various species is no less
than 60%, while it does not exceed 30% between the SmAP1 and SmAP2 proteins of
the same organism. It was
shown that SmAP specifically recognizes poly(U) sequences and form complexes
with tRNA but up to now the role of SmAP in the RNA metabolism or regulation
translation in archaea studied rather poor.
In order to study functions
of archaeal Lsm proteins SmAP2 from Methanococcus
vannielii and SmAP from Sulfolobus
acidocaldarius were
chosen. The proteins were isolated and purified. Crystals of proteins
and their complexes with ribonucleotides were obtained. Using the approach, which
was developed in our group, we determined single-stranded RNA-binding sites on
the surface of the proteins. In addition, AMP affinities
to the proteins have been determined by measuring fluorescence changes during titration of the AMP-MANT
solution by appropriate protein.
This
work was supported by Russian Scientific Foundation (project 14-14-00496).