The Structural and Functional Uniqueness of the glmS Ribozyme - Progress in Molecular Biology and Translational Science - page 172

used to investigate interactions between the glmS ribozyme and GlcN6P.
These studies have revealed the essential components of the coenzyme
and the RNA, and they provide evidence for the mechanism of action.

3. BIOLOGICAL FUNCTION OF THE glmS RIBOZYME
The catalytic glmS riboswitch resides in the 5 0 -untranslated region of
the glmS mRNA of numerous Gram-positive bacteria including those men-
tioned in the introduction as well as the emerging superbug Clostridium dif-
ficile . 7-9 The glmS messenger RNA is responsible for producing the GlmS
enzyme, fructose-6-phosphate amidotransferase, which catalyzes a reaction
that produces GlcN6P. 10 The production of this amino sugar is one of the
first steps in a metabolic pathway that ultimately effects synthesis of the bac-
terial cell wall. 10 Therefore, proper regulation of this pathway is important
to the viability of the bacterium. 10,11 The glmS riboswitch/ribozyme selec-
tively recognizes GlcN6P and is 10 6 -10 7 -fold activated by this metabolic
product of the GlmS enzyme. 2,6 The binding of metabolite initiates an inter-
nal phosphoester transfer reaction that results in self-cleavage and inactiva-
tion of the mRNA. RNA inactivation has been shown to involve RNase J1,
a homolog of the E. coli RNase E protein. 5 Therefore, the glmS ribozyme
facilitates feedback inhibition of the metabolic pathway.

4. glmS RIBOZYME UNIQUENESS
The role of GlcN6P as a coenzyme for glmS ribozyme self-cleavage
was first shown biochemically 6 and then biophysically. 12-17 In addition to
kinetic analyses and crystallographic studies with GlcN6P and closely related
analogs, other compounds (including carbasugars) have been shown to stim-
ulate self-cleavage albeit to a lesser degree. 6,18-20 These results lead to the
interesting question of how various ligands may affect glmS self-cleavage
in vivo , as there are many different hexoses varying in concentration within
the cell. Fedor and colleagues demonstrated that levels of hexose metabolites
in yeast can modulate function of the glmS ribozyme through either inhibi-
tion or activation of self-cleavage. 21 Therefore, the glmS riboswitch must
integrate chemical signals from a number of sources to tune gene expression
to the metabolic needs of the cell. In order to develop drugs that might act as
antibiotics by targeting the glmS ribozyme, a thorough analysis of all struc-
tural requirements of

the RNA and ligand must be examined and

appreciated.