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.