PT  - JOURNAL ARTICLE
AU  - Nir Fluman
AU  - Victor Tobiasson
AU  - Gunnar von Heijne
TI  - Stable membrane topologies of small dual-topology membrane proteins
AID  - 10.1101/133298
DP  - 2017 Jan 01
TA  - bioRxiv
PG  - 133298
4099  - http://biorxiv.org/content/early/2017/05/02/133298.short
4100  - http://biorxiv.org/content/early/2017/05/02/133298.full
AB  - The topologies of α-helical membrane proteins are generally thought to be determined during their cotranslational insertion into the membrane. It is typically assumed that membrane topologies remain static after this process has ended. Recent findings, however, question this static view by suggesting that some parts of, or even the whole protein, can reorient in the membrane on a biologically relevant time scale. Here, we focus on anti-parallel homo-or hetero-dimeric Small Multidrug Resistance proteins, and examine whether the individual monomers can undergo reversible topological inversion (flip-flop) in the membrane until they are trapped in a fixed orientation by dimerization. By perturbing dimerization using various means, we show that the membrane topology of a monomer is unaffected by the presence or absence of its dimerization partner. Thus, membrane-inserted monomers attain their final topologies independently of dimerization, suggesting that wholesale topological inversion is an unlikely event in vivo.