Conservation of the Major Cold Shock Protein in Lactic Acid Bacteria
Woojin S. Kim, Nongpanga Khunajakr, Jun Ren, Noel W. Dunn
Department of Biotechnology, The University of New South Wales, Sydney, NSW 2052, Australia
Received: 1 April 1998 / Accepted: 16 June 1998
Abstract. Primers designed from consensus regions of the major cold shock gene of different bacterial
species were used in PCR amplification of Lactic Acid Bacteria (LAB). An appropriately-sized PCR
product was obtained from Lactococcus lactis subsp. lactis LL43-1 and MG1363; Lactococcus lactis
subsp. cremoris LC10-1, LC11-1, and LC12-1; Streptococcus thermophilus ST1-1; Enterococcus faecalis
EF1-1; Lactobacillus acidophilus LA1-1; Lactobacillus helveticus LH1-1; Pediococcus pentosaceus
PP1-1; and Bifidobacterium animalis BA1-1. The PCR products were cloned and sequenced. The deduced
amino acid sequences displayed high sequence similarity with the major cold shock proteins of
Escherichia coli and Bacillus subtilis and the human Y-box factor. The amino acid residues of the cold
shock domain implicated in nucleic acid binding in several unrelated species were also highly conserved
in the LAB strains. It is possible, therefore, that this protein in LAB may also act as a transcriptional
enhancer to other cold shock genes and/or act as an RNA chaperone unwinding tightly folded RNA
molecules.
Cold shock-induced proteins have been identified in a
number of different organisms, including Escherichia
coli [4] and Bacillus subtilis [19], and they have been
implicated in the adaptive processes required for cell
viability at low temperatures [7]. The major cold shock
proteins of E. coli (CspA) and B. subtilis (CspB) have
been characterized. These small hydrophilic proteins
consist of 70 and 67 amino acids respectively, and share
about 61% sequence homology [19]. These proteins also
show high sequence homology (43%) with the Y-box
factors [19], which are a family of eukaryotic nucleic
acid-binding proteins. The domain of these proteins
involved in the nucleic acid binding is referred to as the
cold shock domain. The domain preferentially binds to
the Y-box, which is an element in the promoter region of
mammalian major histocompatibility complex class II
genes. The Y-box is characterized by the highly con-
served sequence ATTGG [20]. This sequence has also
been shown to exist in the promoter regions of at least
two cold shock genes, hns [11] and gyrA [8]. hns encodes
the nucleoid protein H-NS, and gyrA encodes the ␣
subunit of DNA gyrase. It has been demonstrated that
CspAbinds to theATTGG element in the promoter region
of gyrA [8]. It has also been demonstrated that CspB
binds to single-stranded DNA that contains the ATTGG
element as well as the complementary CCAAT sequence
[5]. Therefore, it has been suggested that CspA and CspB
could act as a transcriptional enhancer to cold shock
genes by recognizing the putative ATTGG sequence.
Further evidence of the protein–nucleic acid interac-
tion comes from the three-dimensional structures of
CspAandCspB, which have been determined by 2D-NMR
and X-ray studies [15–17]. First, the two structures were
found to be very similar. Second, it was revealed that the
surface of the proteins is rich in aromatic and basic amino
acid residues characteristic of proteins that interact with
nucleic acids. Third, it was revealed that the proteins
contain sequence motifs typical of RNA-binding pro-
teins. It has been suggested that the highly conserved
amino acids located at the binding site (Lys
7
,Trp
8
,Lys
13
,
Phe
15
, Phe
17
, Phe
27
, His
29
, Phe
30
, Phe
38
, and Arg
56
)of
CspB, as well as the corresponding amino acids of CspA
and Y-box factors, are involved in DNA binding and
possibly also in RNA binding [13, 16].
Although the major cold shock protein has been
studied in E. coli and B. subtilis, little is known in the
industrially important lactic acid bacteria, despite the
Correspondence to: W.S. Kim
C
URRENT
M
ICROBIOLOGY
Vol. 37 (1998), pp. 333–336
An International Journal
Springer-Verlag New York Inc. 1998