Alan J. Waring*, Alessandro Mastrogiacomo+, and Cameron B. Gundersen*
Department of Pediatrics*, Department of Molecular Pharmacology and the Brain Research Institute+, UCLA School of Medicine, Los Angeles, CA 90024, USA
Cysteine-string proteins (cps) are novel, approximately 20 kD, heavily lipidated components of nerve endings and synaptic vesicles in a number of species including Drosophila (insect), Torpedo (fish), and rat (Mastrogiacomo and Gundersen, 1995). Csps are tethered to membranes via palmitoyl residues that are esterified to the majority of the cysteines of the cysteine string. To investigate the secondary structure of these highly amphipathic proteins, we used CD and FTIR spectroscopy in several structure-promoting environments. Purified native protein from fish (solubilized in a buffer containing Triton X-100) has a dominant helical component in its spectrum. Similarly, a recombinant form of rat csp that lacks the cysteine string displays CD spectra with dichroic minima at 208 and 222 nm. These minima are characteristic of highly helical proteins. However, FTIR studies of a synthetic peptide corresponding to the cysteine-string domain of Torpedo csp revealed a major band at 1630 cm-1 and a minor band at 1693 cm-1 in DMSO or in trifluoroethanol. These absorbances are typical of anti-parallel [[beta]]-sheet conformations. Taken together, these observations suggest that csps have a dominant alpha helical conformation in detergent membrane-mimic systems. In contrast, peptides representing the cysteine-rich region appear largely to assume a [[beta]]-sheet conformation in structure-promoting solvents.
1. Mastrogiacomo, A. & Gundersen, C.B. (1995) Molecular Brain Res 28, 12-18.