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Similar amounts of ribosomal and translation-specific proteins have also
been revealed in mesophilic fast-growing bacteria, such as B. subtilis or
B. licheniformis , under optimal growth conditions ( Buttner et al., 2001;
Voigt et al., 2004; Wilmes et al., 2011 ), suggesting that also the expression
of these proteins, directly related to protein synthesis, is likely growth-rate
dependent ( Klumpp, Zhang, & Hwa, 2009 ).
Basedon the cytoplasmic proteome and the available genome sequence, the
analysis of the amino acid degradation pathways showed that all the common
degradation routes are present in Ph TAC125, with the exception of those
involved in Trp and Lys catabolism ( Wilmes et al., 2011 ). Since the Antarctic
genome contains coding sequences of biosynthetic enzymes for all
20 proteinogenic amino acids, it is likely that the degradation of Trp and Lys
occurs by reversal of the biosynthetic routes. For instance, an alternative way
to use Lys may be decarboxylation to cadaverine via PSHAa1094 (annotated
as a putative basic amino acid decarboxylase) ( Wilmes et al., 2011 ). Further, a
relatively high abundance of the tricarboxylic acid cycle enzymes in the cyto-
plasmic proteome analysed at 16 C, needed for efficient catabolism of the
peptone-based amino acids, is in line with the extremely high growth rate
(maximal rate being 0.35 h 1 ) of theAntarctic bacterium( Wilmes et al., 2011 ).
The major CAP, 37-fold over-expressed at 4 C( Piette et al., 2010 ), is the
TF Tig, a CSP in E. coli ( Kandror &Goldberg, 1997 ). TF is the first molecular
chaperone interacting with virtually all newly synthesised polypeptides on
the ribosome; it assists folding by delaying premature chain compaction
and maintaining the elongating polypeptide in a non-aggregated state until
adequate structural information for correct folding is available, and later
promotes protein folding ( Hartl & Hayer-Hartl, 2009; Martinez-Hackert &
Hendrickson, 2009; Merz et al., 2008 ). TF also possesses a peptidyl-prolyl
cis - trans isomerase activity ( Kramer et al., 2004 ), the rate-limiting step in
the folding of a wide range of proteins ( Baldwin, 2008 ). In Ph TAC125,
the peptidyl-prolyl cis - trans isomerase involved in protein folding is
up-regulated at low temperature ( Piette et al., 2010 ).
The major heat-shock proteins (HSPs), such as the chaperone DnaK, the
chaperonin GroEL/ES and the chaperone Hsp90, are cold-repressed in the
proteome of Ph TAC125. However, their expression is up-regulated when
the bacterium is grown at higher temperature, indicating heat-induced cel-
lular stress ( Goodchild et al., 2005; Rosen & Ron, 2002 ). Synthesis of HSPs
is also repressed during growth at low temperatures ( Kandror & Goldberg,
1997 )in E. coli . Accordingly, the observed cold repression of HSPs would be
beneficial not only to Ph TAC125 but also to E. coli .
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