 |
PDBsum entry 1pl5
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
DNA binding protein/transcription
|
PDB id
|
|
|
|
1pl5
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
 |
Contents |
 |
|
|
|
|
|
|
|
|
|
|
* Residue conservation analysis
|
|
|
|
|
References listed in PDB file
|
|
|
Key reference
|
|
|
Title
|
|
The sir4 c-Terminal coiled coil is required for telomeric and mating type silencing in saccharomyces cerevisiae.
|
|
|
Authors
|
|
G.A.Murphy,
E.J.Spedale,
S.T.Powell,
L.Pillus,
S.C.Schultz,
L.Chen.
|
|
|
Ref.
|
|
J Mol Biol, 2003,
334,
769-780.
[DOI no: ]
|
|
|
PubMed id
|
|
|
|
|
|
Abstract
|
|
|
Saccharomyces cerevisiae Sir4p plays important roles in silent chromatin at
telomeric and silent mating type loci. The C terminus of Sir4p (Sir4CT) is
critical for its functions in vivo because over-expression or deletion of Sir4CT
fragments disrupts normal telomeric structure and abolishes the telomere
position effect. The 2.5A resolution X-ray crystal structure of an Sir4CT
fragment (Sir4p 1217-1358) reveals a 72 residue homodimeric, parallel coiled
coil, burying an extensive 3600A(2) of surface area. The crystal structure is
consistent with results of protein cross-linking and analytical
ultracentrifugation results demonstrating that Sir4CT exists as a dimer in
solution. Disruption of the coiled coil in vivo by point mutagenesis results in
total derepression of telomeric and HML silent mating marker genes, suggesting
that coiled coil dimerization is essential for Sir4p-mediated silencing. In
addition to the coiled coil dimerization interface (Sir4CC interface), a
crystallographic interface between pairs of coiled coils is significantly
hydrophobic and buries 1228A(2) of surface area (interface II). Remarkably,
interface II mutants are deficient in telomeric silencing but not in mating type
silencing in vivo. However, point mutants of interface II do not affect the
oligomerization state of Sir4CT in solution. These results are consistent with
the hypothesis that interface II mimics a protein interface between Sir4p and
one of its protein partners that is essential for telomeric silencing but not
mating type silencing.
|
|
|
|
|
|
|
|
Figure 1.
Figure 1. The X-ray crystal structure of Sir4p residues
1272-1347. (a) Two C-terminal Sir4 fragments combine to form a
72 residue homodimeric parallel coiled coil, including amino
acid residues V1274 to L1344 (strand A, cyan) or M1345 (strand
S, magenta). Residues in positions a and d are drawn in stick
model. (b) A helical wheel diagram with a and d residues listed.
b-Branching residues are shown in bold, colored are charged or
polar residues (d positions K1288, N1309, T1323, and K1337). (c)
Residues in the coiled coil. Mutations to disrupt the coiled
coil are in bold, and underlined when combined. Interface II
mutants are red.
|
|
Figure 4.
Figure 4. A large hydrophobic interface exists between
symmetry-related coiled coils. (a) The surface of the N terminus
of the coiled coil (NT-surface) (green and rose) contacts a
C-terminal surface of its symmetry-related neighbor (CT-surface)
(cyan and magenta). This interface, interface II, has a
hydrophobic core, seven ordered water molecules and a hydrogen
bonding network. For clarity, only hydrogen bonding involving
water molecules is shown. (b) Surface complementarity of
interface II. A coiled coil's NT-surface (molecular surface
representation) has a large hole into which Phe1322 from another
coiled coil's CT-surface nestles (cyan and magenta). Interface
residues from the CT-surface are shown. (c) and (d) Molecular
surfaces colored by hydrophobicity (F, V, I, L, A are yellow)
show the two interaction surfaces. A stick model is placed atop
the surface representation to indicate the position of the
interface. (c) The NT-surface. (d) The CT-surface.
|
|
|
|
|
|
The above figures are
reprinted
by permission from Elsevier:
J Mol Biol
(2003,
334,
769-780)
copyright 2003.
|
|
|
|
|
|
|
