UCSF

Open & shut case: Thomaston's paper in JACS

The M2 channel S31N mutant seen adopting both conformations within the same crystal lattice

A team headed by DGL's Jessica Thomaston (recent PhD, now post-doc w/ M. Caffrey) published work in the Journal of the American Chemical Society characterizing reasons for drug resistance for one of the major mutant strains of the Influenza flu virus via the M2 channel protein. Two major conformations of the M2 channel have been observed, OPEN & CLOSED, key for acid-sensing and proton transport functions allowing the flu virus to infect the host cell.  Thomaston previously elucidated (Protein Science) how the S31N M2 mutant prevents binding of 'channel blocker' drugs in the OPEN state. Her new crystal structure shows both the closed and the open conformation existing simultaneously. Two key lessons about the M2 channel come as a result.

 

The first lesson is that CLOSED conformation of the S31N mutant also seems poorly adapted to bind traditional M2-based flu drugs. The ASN31 amino acid side-chain stabilizes a slightly rotated and newly observed conformation of the channel resulting in a constriction the drug binding pocket.

Changes in the M2 channel closed state due to ASN31 - constriction at A30

 

The second lesson details the transporter-like conformational equilibrium of the M2 channel. Since both OPEN and CLOSED states were observed at 1 to 1 ratio the same crystal, the energetic difference between the two states came into question. Through complementary solution NMR studies, it was shown that both states exist and inter-change at equilibrium - being highly dependent on the pH. This finding provides key structural insights into the acid-dependence of the M2 channel's proton conduction activity, the difficult energetic feat of putting many charged atoms in close proximity to get protons across the membrane.

solution NMR shows the M2 channel's structural dependence of pH

 

See the recently published work here:

Thomaston JL, Wu Y, Polizzi N, Liu L, Wang J, DeGrado WF. X-ray crystal structure of the influenza A M2 proton channel S31N mutant in two conformational states: an open and shut case. JACS. (2019)  Latest articles.
View in: PubMed

 

In collaboration with DGL alumni - Professor Jun Wang (Univ. of Arizona)