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PR01134

Identifier
CONNEXINA4  [View Relations]  [View Alignment]  
Accession
PR01134
No. of Motifs
4
Creation Date
20-APR-1999
Title
Gap junction alpha-4 protein (Connexin37) signature
Database References
PRINTS; PR00206 CONNEXIN
PRODOM; PD020307
INTERPRO; IPR002263
Literature References
1. PHELAN, P., BACON, J.P., DAVIES, J.A., STEBBINGS, L.A., TODMAN, M.G.,
AVERY, L., BAINES, R.A., BARNES, T.M., FORD, C., HEKIMI, S., LEE, R.,
SHAW, J.E., STARICH, T.A., CURTIN, K.D., SUN, Y. AND WYMAN, R.J.
Innexins: a family of invertebrate gap-junction proteins.
TRENDS GENET. 14 348-349 (1998).
 
2. DERMIETZEL, R. AND SPRAY, D.C.
Gap junctions in the brain: where, what type, how many and why?
TRENDS NEUROSCIENCE 16 186-192 (1993).
 
3. GOODENOUGH, D.A., GOLIGER, J.A. AND PAUL, D.L.
Connexins, connexons, and intercellular communication.
ANNU.REV.BIOCHEMISTRY 65 475-502 (1996).
 
4. KUMAR, N.M. AND GILULA, N.B.
The gap junction communication channel.
CELL 84 381-388 (1996).
 
5. KUMAR, N.M. AND GILULA, N.B.
Molecular biology and genetics of gap junction channels.
SEMIN.CELL BIOL. 3 3-16 (1992).
 
6. NICHOLSON, S.M. AND BRUZZONE, R.
Gap junctions: getting the message through.
CURR.BIOL. 7 340-344 (1997).
 
7. SIMON, A.M. AND GOODENOUGH, D.A.
Diverse functions of vertebrate gap junctions.
TRENDS CELL BIOL. 8 477-483 (1998).
 
8. SPRAY, D.C. AND DERMIETZEL, R.
X-linked dominant Charcot-Marie-Tooth disease and other potential gap-
junctions diseases of the nervous system.
TRENDS NEUROSCIENCE 18 256-262 (1995).

Documentation
The connexins are a family of integral membrane proteins that oligomerise
to form intercellular channels that are clustered at gap junctions. These
channels are specialised sites of cell-cell contact that allow the passage
of ions, intracellular metabolites and messenger molecules (with molecular
weight <1-2 kDa) from the cytoplasm of one cell to its apposing neighbours.
They are found in almost all vertebrate cell types, and somewhat similar
proteins have been cloned from plant species. Invertebrates utilise a 
different family of molecules, innexins, that share a similar predicted 
secondary structure to the vertebrate connexins, but have no sequence 
identity to them [1].
 
Vertebrate gap junction channels are thought to participate in diverse
biological functions. For instance, in the heart they permit the rapid 
cell-cell transfer of action potentials, ensuring coordinated contraction 
of the cardiomyocytes. They are also responsible for neurotransmission at
specialised `electrical' synapses. In non-excitable tissues, such as the 
liver, they may allow metabolic cooperation between cells. In the brain,
glial cells are extensively-coupled by gap junctions; this allows waves of
intracellular Ca2+ to propagate through nervous tissue, and may contribute
to their ability to spatially-buffer local changes in extracellular K+ 
concentration [2].
 
The connexin protein family is encoded by at least 13 genes in rodents, with
many homologues cloned from other species. They show overlapping tissue 
expression patterns, most tissues expressing more than one connexin type.
Their conductances, permeability to different molecules, phosphorylation and
voltage-dependence of their gating, have been found to vary. Possible
communication diversity is increased further by the fact that gap junctions
may be formed by the association of different connexin isoforms from 
apposing cells. However, in vitro studies have shown that not all possible
combinations of connexins produce active channels [3,4].
 
Hydropathy analysis predicts that all cloned connexins share a common
transmembrane (TM) topology. Each connexin is thought to contain 4 TM
domains, with two extracellular and three cytoplasmic regions. This model
has been validated for several of the family members by in vitro biochemical
analysis. Both N- and C-termini are thought to face the cytoplasm, and the
third TM domain has an amphipathic character, suggesting that it contributes
to the lining of the formed-channel. Amino acid sequence identity between
the isoforms is ~50-80%, with the TM domains being well conserved. Both
extracellular loops contain characteristically conserved cysteine residues,
which likely form intramolecular disulphide bonds. By contrast, the single 
putative intracellular loop (between TM domains 2 and 3) and the cytoplasmic
C-terminus are highly variable among the family members. Six connexins are
thought to associate to form a hemi-channel, or connexon. Two connexons then
interact (likely via the extracellular loops of their connexins) to form the
complete gap junction channel.
 
Two sets of nomenclature have been used to identify the connexins.  The
first, and most commonly used, classifies the connexin molecules according
to molecular weight, such as connexin43 (abbreviated to Cx43), indicating
a connexin of molecular weight close to 43 kDa. However, studies have
revealed cases where clear functional homologues exist across species
that have quite different molecular masses; therefore, an alternative
nomenclature was proposed based on evolutionary considerations, which
divides the family into two major subclasses, alpha and beta, each with a
number of members [5]. Due to their ubiquity and overlapping tissue
distributions, it has proved difficult to elucidate the functions of
individual connexin isoforms. To circumvent this problem, particular
connexin-encoding genes have been subjected to targeted-disruption in mice,
and the phenotype of the resulting animals investigated. Around half the
connexin isoforms have been investigated in this manner [6,7]. Further
insight into the functional roles of connexins has come from the discovery
that a number of human diseases are caused by mutations in connexin genes.
For instance, mutations in Cx32 give rise to a form of inherited
peripheral neuropathy called X-linked dominant Charcot-Marie-Tooth disease
[8]. Similarly, mutations in Cx26 are responsible for both autosomal
recessive and dominant forms of nonsyndromic deafness, a disorder
characterised by hearing loss, with no apparent effects on other organ
systems.
 
Gap junction alpha-4 protein (also called connexin37, or Cx37) is a connexin
of 333 amino acids (human isoform) with a predicted molecular mass of ~37
kDa. It is expressed in many organs and tissues, including: brain, heart,
uterus, ovary, and endothelial cells of blood vessels. When heterologously
expressed, Cx37 forms intercellular channels that are more sensitive to
voltage and show faster voltage-gating kinetics than most other previously-
characterised gap junction channels. The recent generation of mice lacking
the gene encoding Cx37 (GJA4 or CXN-37) has shed some light on its function
in vivo. Female mice lacking Cx37 are viable and apparently in good health,
but are rendered infertile, as a result of a failure to ovulate. It appears
that in the ovarian follicle, functional gap junctions (formed by Cx37) are
critical for communication between the oocyte and the surrounding granulosa
cells. Without Cx37, follicular development is arrested, and subsequently
ovulation does not occur.
 
CONNEXINA4 is a 4-element fingerprint that provides a signature for the
gap junction alpha-4 protein. The fingerprint was derived from an initial
alignment of 3 sequences: the motifs were drawn from conserved regions
spanning virtually the full alignment length, focusing on those regions
that characterise the gap junction alpha-4 isoform but distinguish it from
others - motif 1 resides within the putative cytoplasmic loop between TM
domains 2 and 3; motif 2 encodes most of the third putative TM domain; and
motifs 3-4 lie within the cytoplasmic C-terminus. A single iteration on
SPTR37_9f was required to reach convergence, no further sequences being
identified beyond the starting set.
Summary Information
3 codes involving  4 elements
0 codes involving 3 elements
0 codes involving 2 elements
Composite Feature Index
43333
30000
20000
1234
True Positives
CXA4_HUMAN    CXA4_MOUSE    CXA4_RAT      
Sequence Titles
CXA4_HUMAN  GAP JUNCTION ALPHA-4 PROTEIN (CONNEXIN 37) (CX37) - HOMO SAPIENS (HUMAN). 
CXA4_MOUSE GAP JUNCTION ALPHA-4 PROTEIN (CONNEXIN 37) (CX37) - MUS MUSCULUS (MOUSE).
CXA4_RAT GAP JUNCTION ALPHA-4 PROTEIN (CONNEXIN 37) (CX37) - RATTUS NORVEGICUS (RAT).
Scan History
SPTR37_9f  1  300  NSINGLE    
Initial Motifs
Motif 1  width=9
Element Seqn Id St Int Rpt
PSKDPHVER CXA4_RAT 116 116 -
PSKDLHVER CXA4_MOUSE 116 116 -
PAKDPQVER CXA4_HUMAN 116 116 -

Motif 2 width=14
Element Seqn Id St Int Rpt
GTYVISVLCKSVLE CXA4_RAT 152 27 -
GTYVVSVLCKSVLE CXA4_MOUSE 152 27 -
GTYVASVLCKSVLE CXA4_HUMAN 152 27 -

Motif 3 width=8
Element Seqn Id St Int Rpt
QGSASDPY CXA4_RAT 251 85 -
QGSASDPY CXA4_MOUSE 251 85 -
QGTSSDPY CXA4_HUMAN 251 85 -

Motif 4 width=8
Element Seqn Id St Int Rpt
NLTTEERL CXA4_RAT 292 33 -
NLTTEERL CXA4_MOUSE 292 33 -
NLTTEERL CXA4_HUMAN 292 33 -
Final Motifs
Motif 1  width=9
Element Seqn Id St Int Rpt
PSKDPHVER CXA4_RAT 116 116 -
PSKDLHVER CXA4_MOUSE 116 116 -
PAKDPQVER CXA4_HUMAN 116 116 -

Motif 2 width=14
Element Seqn Id St Int Rpt
GTYVISVLCKSVLE CXA4_RAT 152 27 -
GTYVVSVLCKSVLE CXA4_MOUSE 152 27 -
GTYVASVLCKSVLE CXA4_HUMAN 152 27 -

Motif 3 width=8
Element Seqn Id St Int Rpt
QGSASDPY CXA4_RAT 251 85 -
QGSASDPY CXA4_MOUSE 251 85 -
QGTSSDPY CXA4_HUMAN 251 85 -

Motif 4 width=8
Element Seqn Id St Int Rpt
NLTTEERL CXA4_RAT 292 33 -
NLTTEERL CXA4_MOUSE 292 33 -
NLTTEERL CXA4_HUMAN 292 33 -