Cystic Fibrosis revisited: An Indepth look at the CFTR Protein

Prior Knowledge:

To Review.....

Cystic fibrosis is the most common fatal genetic disease in the United States today. CF causes the body to produce a thick, sticky mucus that clogs the lungs, leading to infection.

The affected protein is CFTR (cystic fibrosis transmembrane conductance regulator). The tertiary structure of CFTR consists of four domains: two are membrane binding and two ATP-binding.

An Artist's Rendering of the CFTR Protein:

Protein Family: ATP-Binding Cassette (ABC) superfamily, sub-family C, member 5

accession # AAB71758

Entrez Gene Link

Domains: 1. Highly conserved ATP binding cassette (ABC)

2. Less conserved Transmembrane domain

CFTR functions as a dimer and therefore constitutes four domains, two ABC modules and two transmembrane domains.

ABC transporters are involved in the export or import of a wide variety of substrates ranging from small ions to macromolecules. CFTR faciliates the movement of chlorine ions.

(Expasy-ScanProsite Tool) http://us.expasy.org/cgi-bin/nicedoc.pl?PDOC00185

To Summarize...CFTR Contains Five Structural Domains:
Two hydrophilic Nucleotide binding domains (NBD1 and NBD2)
Two hydrophobic Transmembrane domains
One Regulatory domain (R)

(CDD @ NCBI) http://www.ncbi.nlm.nih.gov/Structure/cdd/wrpsb.cgi?INPUT_TYPE=precalc&SEQUENCE=5685864

Nucleotide Binding Domain 1
· Spans 157 amino acids
· Includes Walker A
· Includes Walker B
· Includes A linkerA C
· Seven alpha helices
· Seven beta sheet regions

Picture of the Phosphorylated CFTR ND1 with ATP

Nucleotide Binding Domain 2
· High amount of homology with NBD1
· Includes Walker A region
· Includes Walker B region
· Includes A linkerA region C
· Predicted to contain seven alpha helices
· As well as, seven beta sheet regions

PDB SUM @ EBI

Secondary Structure

Transmembrane Domains

-Hydrophobic region of CFTR

-Forms a channel for Cl- movement through the cell
-Can regulate Cl- by altering pore size. Many mutations occur in these domains which can lead to a decrease in ion selectivity

Primary Structural Analysis of CFTR

ProtoParam @ Expasy to determine Physical and Chemical Parameters for a given protein:

Computed parameters include the molecular weight, theoretical pI, amino acid composition, atomic composition, extinction coefficient, estimated half-life, instability index, aliphatic index and grand average of hydropathicity (GRAVY).


Computed Parameters of inputed amino acid sequence for CFTR, Homo Sapiens:

Number of amino acids: 1436

Molecular weight: 160856.6

Total number of negatively charged residues (Asp + Glu): 151

Total number of positively charged residues (Arg + Lys): 164

Atomic composition: Carbon C 7228Hydrogen H 11538Nitrogen N 1954Oxygen O 2068Sulfur S 61

Formula: C7228H11538N1954O2068S61

Total number of atoms: 22849

http://us.expasy.org/cgi-bin/protparam

Homologous Proteins?

CDART: Conserved Domain Architecture Retrieval Tool

CDART Results

Gene Ontology of CFTR @ the Gene Ontology Consortium

Cellular Component- integral to plasma membrane

Biological Process- transport

Molecular Function- ATP binding