MNA-C12. It's not just a part of fighting influenza.
It's a part of setting high standards.

Influenza is an infectious disease which is estimated to be responsible for the deaths of 291,000 – 646,000 people worldwide(1). The first step in the influenza infection life cycle is the binding of the glycoprotein hemagglutinin (HA) to sialic acid found on the host cell membrane(2). This process allows for the fusion of the influenza virus with the host cells. A number of x-ray crystal structures of the HA glycoprotein have been determined, but no structures to date are of the full-length protein containing the transmembrane domain.
 
In September 2018, the labs of Steven Gamblin, Peter Rosenthal, and John Skehel at the Francis Crick Institute in London have determined the Cryo-EM structures of both the full-length HA protein and the HA protein in complex with a Fab of a neutralizing antibody(3). These structures show that the transmembrane domain is linked to the rest of the protein via flexible linkers. In the structure of the HA-Fab complex, the Fab binds near these linkers, restricting flexibility. These results suggest that flexibility in this linker region may be necessary for Influenza infection and a target for future therapeutic development.

In this study, the full-length HA protein was solubilized using 1% LDAO, and exchanged into 0.01% LMNG during purification for Cryo-EM structure determination. For the full-length HA-Fab complex, HA was solubilized in 1% LDAO and exchanged into 0.05% DDM during purification. Upon addition of the Fab fragment, 0.1% MNA-C12 was added, and the HA-Fab complex was further purified using gel filtration in 0.002% MNA-C12. LMNG and MNA-C12 were used in these structures for their ability to preserve the structure of the membrane proteins. To our knowledge, the HA-Fab complex represents the first structure determined using MNA-C12.


Mannitol-Based Amphiphiles (MNA) detergents:  A variation on a theme.

First developed in 2016 by the labs of Brian Kobilka and Pil-Seok Chae, the MNA class of detergents are a variation to the neopentyl glycol class of detergents(4). MNA-C12 has two flexible twelve carbon alkyl chains connected to four glucose groups via a mannitol linker. Compared to DDM and LMNG, the CMC of MNA-C12 is 17.4 fold lower than DDM and 2 fold lower than LMNG (DDM: 0.0087%, LMNG: 0.001%, MNA-C12: 0.0005%). In this original characterization of the MNA detergents, it was hypothesized that due to the strong binding affinity, small protein-detergent complex size, and improved protein stabilization, these detergents would be suitable for the electron microscopy analysis of membrane proteins. This recent Cryo-EM structure of the HA-Fab complex and the use of MNA-C12 confirms this hypothesis.


   
References:
  1. Centers for Disease Control and Prevention. Seasonal flu death estimate increases worldwide. December 13, 2017 Press Release.
  2. Samji, T. (2009) Yale J Biol Med. 82(4): 153-159.
  3. Benton, D.J. et al. (2018) PNAS. 115(40) 10112-10117.
  4. Hussain, H. et al. (2016) Chem. Eur. J. 22(21) 7068-7073.