Documents
Resources
Learning Center
Upload
Plans & pricing Sign in
Sign Out

The NBD Domain of the Cystic Fibrosis Transmembrane Conductance

VIEWS: 17 PAGES: 12

									The NBD1 Domain of the Cystic Fibrosis
Transmembrane Conductance Regulator




          Image made using pymol & PDB 1QH3 from Lewis,
                    EMBO,23,2,283-293,2004




            By Eladio Abreu
           Cystic Fibrosis
Cystic Fibrosis (CB) is a lethal autosomal
recessive genetic disease
Symptoms:
– mucus build up
– debilitating chronic pulmonary inflammation
  and blockage
– excess loss of salts in sweat
– reduced pancreatic enzyme release
Reduced life span
   Source: Defective CFTR
Dysfunctional chloride ion transport in
epithelial cells is responsible for the
disease
 A defect in the cystic fibrosis
transmembrane conductance regulator
(CFTR) protein leads to the obvious
transport problem
               CFTR
The CFTR was first identified in 1989

Sequence analysis predicted that it was
comprised of:
– 2 MSDs
– 2 NBDs
– 1 R-region
 Characteristics consistent with members
of the ABC super family of membrane
transporters.
                                                   MSD1                MSD2


Thought to satisfy
binding interactions                                       L
of ATP bound to                        N                 S
                                                                 ATP
NBD2                                                     G
                                                           G
                                                             Q         H
                                                 NBD1                      G    NBD2
                                                                 ATP        H
                                                                            S
                                                                           L
                                                                                       C
                       Signature                                 R
                       Sequence


                               ATP


                                                      Model for The Cystic Fibrosis
                                                     Trans-Membrane Regulator, and
                                                        Position of NBD1 Within it
               NBD1
                                   Image made using pymol,powerpoint & PDB 1QH3 from Lewis,
                                                   EMBO,23,2,283-293,2004
  NBD1 and its Significance
In most ABC transporters ATP hydrolysis cycles
between the 2 NBDs lead to confirmational
changes in the MSDs and subsiquent channel
gating.

NBDs have several structural motifs that aid in
ATP binding and hydrolysis.

All of the mutations that lead to CF are in NBD1
of the CFTR
Tertiary Structure and Subdomain Composition of
                     mNBD1

F1-type ATP binding core                  c
ABC ά-subdomain

β-subdomain

Unique to mNBD1
                                      N
mNBD1




                           Image made using pymol, powerpoint & PDB 1QH3 from
                                    Lewis, EMBO,23,2,283-293,2004
ATP Binds between helices Hl, H1B, and
                H1C
Walker motif A (GSTGSGKTS) extends from the N-
terminal end of H1.
– ATP directly binds:Gly463, Ser466, Gly461, Ser462, and
  Lys464 of walker motif A.
– also binds with the nucleotide indirectly by coordinating
  Mg+2 . Mg+2 is coordinated by Thr465 of Walker Motif A
Walker motif B (LYLLDSPFG) which extends from the
S7 β-strand of the F1-type ATP binding core provides an
ASP residue which aids in Mg+2 coordination

Glu493 from an adjacent Q-loop contributes toward
Mg+2 coordination.

Phe430 of helix H1C makes an edge to face interaction
with the adenine of ATP.
Position and Mode of
ATP Binding in
mNBD1




                                       Image made using pymol & PDB 1QH3 from Lewis,
                                                 EMBO,23,2,283-293,2004

                                          The image above identifies the H-
                                          bonding, ionic and Vander Vaals
                                          interactions responsible for binding
                                          ATP to NBD1


             General position of ATP
             binding site
mNBD1 Binds ATP but does not
        hydrolize it
 Structural characteristics    Structural Differences in
shared with other ABC NBDs     mNBD1 that eliminate
implicated in ATP binding      hydrolytic activity


ATP Binding core
 – Walker motifs A and B        – Catalytic charged residues in
 – Q and H loops                  these motifs replaced by
                                  inactive serine residues.




                               ATP only has face to edge
ATP stacks against several     interaction with a PHE residue as
aromatic residues when bound   result to a different torsional
                               angle
CF mutations are not in positions
   involved in ATP hydrolysis


                        ATP binding site




                Image made using pymol & PDB 1QH3 from Lewis,
                          EMBO,23,2,283-293,2004

      Positions of the common CB causative mutations are
   highlighted in cyan, the most common (occurring in 90% of
   CB patients) is the deletion of Phe508 (highlighted in green)
           Conclusions
NBD1 binds ATP but does not hydrolyze it.
CFTR channel gating is dependent on
ATP binding at NBD1 but not its
hydrolysis.
 The NBDS come together to form a
nucleotide sandwich, below the MSDs (as
seen in slide number 5).

								
To top