Phase labeling of C−H and C−C spin-system topologies: Application in constant-time PFG-CBCA(CO)NH experiments for discriminating amino acid spin-system types

✍ Scribed by Carlos B. Rios; Wenqing Feng; Mitsuru Tashiro; Zhigang Shang; Gaetano T. Montelione

• Publisher: Springer Netherlands
• Year: 1996
• Tongue: English
• Weight: 500 KB
• Volume: 8
• Category: Article
• ISSN: 0925-2738
• DOI: 10.1007/bf00410332

✦ Synopsis

Triple-resonance experiments facilitate the determination of sequence-specific resonance assignments of medium-sized ~3C]SN-enriched proteins. Some triple-resonance experiments can also be used to obtain information about amino acid spin-system topologies by proper delay tuning. The constant-time PFG-CBCA(CO)NH experiment allows discrimination between five different groups of amino acids by tuning (phase labeling) independently the delays for proton-carbon refocusing and carbon-carbon constanttime frequency labeling. The proton-carbon refocusing delay allows discrimination of spin-system topologies based on the number of protons attached to C a and C ~ atoms (i.e. C-H phase labeling). In addition, tuning of the carbon-carbon constant-time frequency-labeling delay discriminates topologies based on the number of carbons directly coupled to C a and C ~ atoms (i.e. C-C phase labeling). Classifying the spin systems into these five groups facilitates identification of amino acid types, making both manual and automated analysis of assignments easier. The use of this pair of optimally tuned PFG-CBCA(CO)NH experiments for distinguishing five spin-system topologies is demonstrated for the 124residue bovine pancreatic ribonuclease A protein.