In protein transport between organelles, interactions of v- and t-SNARE proteins are required for fusion of protein-containing vesicles with appropriate target compartments. Mammalian SNARE proteins have been observed to interact with NSF and SNAP, and yeast SNAREs with yeast homologues of NSF and SNAP proteins. This observation led to the hypothesis that, despite low sequence homology, SNARE proteins are structurally similar among eukaryotes. SNARE proteins can be classified into two groups depending on whether they interact with SNARE binding partners via conserved glutamine (Q-SNAREs) or arginine (R-SNAREs). Much of the published structural data available is for SNAREs involved in exocytosis (either in yeast or synaptic vesicles). This paper describes circular dichroism, Fourier transform infrared spectroscopy, and dynamic light scattering data for a set of yeast v- and t-SNARE proteins, Vti1p and Pep12p, that are Q-SNAREs involved in intracellular trafficking. Our results suggest that the secondary structure of Vti1p is highly α-helical and that Vti1p forms multimers under a variety of solution conditions. In these respects, Vti1p appears to be distinct from R-SNARE proteins characterized previously. The α-helicity of Vti1p is similar to that of Q-SNARE proteins characterized previously. Pep12p, a Q-SNARE, is highly α-helical. It is distinct from other Q-SNAREs in that it forms dimers under many of the solution conditions tested in our experiments. The results presented in this paper are among the first to suggest heterogeneity in the functioning of SNARE complexes.

The high affinity interleukin-2 receptor is composed of three cell surface subunits, IL-2Rα, IL-2Rβ, and IL-2Rγ. Functional forms of the IL-2 receptor exist, however, that enlist only two of the three subunits. On activated T-cells, the α- and β-subunits combine as a preformed heterodimer (the pseudo-high affinity receptor) that serves to capture IL-2. On a subpopulation of natural killer cells, the β- and γ-subunits interact in a ligand-dependent manner to form the intermediate affinity receptor site. Previously, we have demonstrated the feasibility of employing coiled-coil molecular recognition for the solution assembly of a heteromeric IL-2 receptor complex. In that study, although the receptor was functional, the coiled-coil complex was a trimer rather than the desired heterodimer. We have now redesigned the hydrophobic heptad sequences of the coiled-coils to generate soluble forms of both the pseudo-high affinity and the intermediate affinity heterodimeric IL-2 receptors. The properties of these complexes were examined and their relevance to the physiological IL-2 receptor mechanism is discussed.