{PDOC00342}
{PS00409; PROKAR_NTER_METHYL}
{BEGIN}
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* Prokaryotic N-terminal methylation site *
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A number of bacteria express filamentous adhesins known as pili.  The pili are
polar flexible filaments of about 5.4 nm diameter and  2500 nm average length;
they  consist of a single polypeptide chain (called pilin or fimbrial protein)
arranged in a helical configuration of five subunits per turn in the assembled
pilus.  Gram-negative  bacteria  produce  pilin which are characterized by the
presence of a  very  short  leader  peptide  of 6 to 7 residues, followed by a
methylated N-terminal phenylalanine residue and by a highly conserved sequence
of about 24 hydrophobic residues.  This class of pilin is often referred to as
NMePhe or type-4 pili [1,2].

Recently a number  of  bacterial proteins  have been sequenced which share the
following structural characteristics with type-4 pili [3]:

 a) The N-terminal residue, which  is  methylated, is hydrophobic (generally a
    phenylalanine or a methionine);
 b) The leader peptide is hydrophilic, consists of 5 to  10 residues (with two
    exceptions, see below) and ends with a glycine;
 c) The fifth residue of the mature  sequence is a glutamate which seems to be
    required for the methylation step;
 d) The first twenty residues of the mature sequence are highly hydrophobic.

These proteins are listed below:

 - Four proteins in an operon  involved  in  a general secretion pathway (GSP)
   for  the export  of  proteins (also called the type II pathway) [4].  These
   proteins have  been  assigned  a different gene name in each of the species
   where they have been sequenced:

   Species                     Gene names
   ------------------------    -------------------------
   Aeromonas hydrophila        exeG   exeH   exeI   exeJ
   Erwinia chrysanthemi        outG   outH   outI   outJ
   Escherichia coli            hofG   hofH   yheH   yheI
   Klebsiella pneumoniae       pulG   pulH   pulI   pulJ
   Pseudomonase aeruginosa     xcpT   xcpU   xcpV   xcpW
   Vibrio cholerae             epsG   epsH   epsI   epsJ
   Xanthomonas campestris      xpsG   xpsH   xpsI   xpsJ

 - Vibrio cholerae toxin co-regulated pilin (gene tcpA). This pilin has a much
   longer putative leader peptide (25 residues).
 - Bacillus subtilis comG competence operon  proteins  3,  4,  and 5 which are
   involved for the uptake of DNA by competent Bacillus subtilis cells.
 - ppdA, ppdB and ppdC, three Escherichia coli hypothetical  proteins found in
   the thyA-recC intergenic region.
 - ppdA, a  hypothetical  protein  near  the  groeLS  operon  of   Clostridium
   perfringens. The putative leader peptide is 23 residues long.

We developed a signature  pattern  based on the N-terminal conserved region of
all these proteins.

-Consensus pattern: [KRHEQSTAG]-G-[FYLIVM]-[ST]-[LT]-[LIVP]-E-[LIVMFWSTAG](14)
                    [The residue after the G is methylated]
-Sequences known to belong to this class detected by the pattern: ALL.
-Other sequence(s) detected in Swiss-Prot: NONE.
-Last update: November 1995 / Text revised.

[ 1] Paranchych W., Frost L.S.
     "The physiology and biochemistry of pili."
     Adv. Microb. Physiol. 29:53-114(1988).
     PubMed=2898203
[ 2] Dalrymple B., Mattick J.S.
     "An analysis of the organization and evolution of type 4 fimbrial
     (MePhe) subunit proteins."
     J. Mol. Evol. 25:261-269(1987).
     PubMed=3118043
[ 3] Hobbs M., Mattick J.S.
     "Common components in the assembly of type 4 fimbriae, DNA transfer
     systems, filamentous phage and protein-secretion apparatus: a general
     system for the formation of surface-associated protein complexes."
     Mol. Microbiol. 10:233-243(1993).
     PubMed=7934814
[ 4] Salmond G.P.C., Reeves P.J.
     "Membrane traffic wardens and protein secretion in gram-negative
     bacteria."
     Trends Biochem. Sci. 18:7-12(1993).
     PubMed=8438237

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