Unfolding studies of human adenovirus type 2 fibre trimers - Evidence for a stable domain

Adenovirus fibres an trimeric proteins that protrude from the 12 fivefold v ertices of the virion and are the cell attachment organelle of the virus. T hey consist of three segments: an N-terminal tail, which is noncovalently a ttached to the penton base, a thin shaft carrying 15 amino acid pseudo repe ats, and a C-terminal globular head (or knob) which recognizes the primary cell receptor. Due to their exceptional stability, which allows easy distin ction of native trimers from unfolded forms and folding intermediates, aden ovirus fibres are a very good model system for studying folding in vivo and in vitro. To understand the folding and stability of the trimeric fibres, the unfolding pathway of adenovirus 2 fibres induced by SDS and temperature has been investigated. Unfolding starts from the N-terminus and a stable i ntermediate accumulates that has the C-terminal head and part of the shaft structure (shown by electron microscopy). The unfolded part can be digested away using limited proteolysis, and the precise digestion sites have been determined. The remaining structured fragment is recognized by monoclonal a ntibodies that are specific for the trimeric globular head and therefore re tains a native trimeric structure, Taken together, our results indicate tha t adenovirus fibres carry a stable C-terminal domain, consisting of the kno b with five shaft-repeats.