Demonstration of a tandem pair of complement protein modules in GABA(B) receptor 1a.
We have subcloned and expressed the N-terminal portion of the recently sequenced metabotropic GABA receptor, GABA(B)R1a. This region of the receptor contains a complement protein-like amino acid sequence. The purified 140-residue recombinant protein fragment was soluble and stable. Mass spectrometry indicated formation of four disulfide bonds, as expected if two complement protein modules (CPs, also known as SCRs, Sushi domains) are formed. The circular dichroism spectrum was unusual and characteristic of CPs. Differential scanning calorimetry demonstrated a melting point (64 degrees C), and total enthalpy commensurate with two fully folded domains. We thus conclude that the 1a subtype of the GABA(B) receptor, but not the 1b subtype, contains a pair of CPs and we present a three-dimensional model of this region.
Hawrot
E
E
Department of Molecular Pharmacology, Physiology and Biotechnology, Brown University, Providence, RI 02192, USA.
Xiao
Y
Y
Shi
Q L
QL
Norman
D
D
Kirkitadze
M
M
Barlow
P N
PN
D000595:Amino Acid Sequence; D002152:Calorimetry, Differential Scanning; D002942:Circular Dichroism; D003165:Complement System Proteins / Q000737:chemistry*; D004220:Disulfides / Q000737:chemistry; D006801:Humans; D010446:Peptide Fragments / Q000737:chemistry; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D018080:Receptors, GABA-B / Q000737:chemistry* / Q000235:genetics; D011994:Recombinant Proteins / Q000737:chemistry; D016415:Sequence Alignment; D017421:Sequence Analysis; D017386:Sequence Homology, Amino Acid; D013053:Spectrophotometry
D004220:Disulfides; D010446:Peptide Fragments; D018080:Receptors, GABA-B; D011994:Recombinant Proteins; D003165:Complement System Proteins