Biophysical studies of membrane proteins/peptides. Interaction with ...

particle is 900 nm in length and 6.5 nm wide. It is formed by a single strand of DNA,
about 6400 nucleotides long, encapsulated by a cylindrical protein coat. The protein
coat presents about 3000 copies of the major coat protein (mcp or gp8), the product of
gene VIII. In addition to mcp, four other coat proteins are present in few copies, capping
the ends of the bacteriophage.
During the infection process, parental coat proteins are embedded in the membrane
while the viral DNA is released in the cytoplasm (see Figure II-1). New copies of mcp
are synthesized in the host and inserted in the membrane, where they are processed by a
leader peptidase (Kuhn et al., 1986). After peptidase action, the C-terminus of mcp is
oriented to the cytoplasm and the N-terminus is located in the periplasm. In the mature
form, mcp is a polypeptide chain 50 aminoacids long and presents a single
transmembrane domain. During the reproductive cycle of the bacteriophage, coat
proteins are stored at very high local levels and finally assembled around viral DNA
into new phage particles (Hemminga et al., 1992).
Figure II-1: Representation of the reproductive cycle of bacteriophage M13 (taken from Spruijt et
al., 1999).
mcp presents three distinct domains which are expected to be related to the distinct
type of interactions that this protein is involved in during the reproductive cycle of the
bacteriophage. In this way, the negatively charged region in the N-terminal domain of
the protein (residues 1-20), rich in glutamate and aspartate, forms the outer hydrophilic
surface of the virus particle. The hydrophobic central domain (residues 21-39) is
responsible for the tight membrane interaction of the membrane form of mcp and for the
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