Insertion Properties of Marginally Hydrophobic Helices in the LacY Lactose Permease Transporter

• Transmembrane helices are generally believed to be recognized individually by the translocon based on theirhydrophobicity, but it has been proposed that they could also be recognized as pairs of helices. The fact thatmost transmembrane helices are individually clearly hydrophobic seems to support separate helix insertion,but there are important exceptions where the helices are only borderline hydrophilic, at least according tosequence-based prediction. Conrming these patterns and characterizing their role for insertion of helices isan important part in deciphering membrane protein insertion and folding. Here, we use a combination ofsequence bioinformatics, simplied physical modeling, and experiments to investigate whether helices in theLacY lactose permease transporter are recognized by the translocon, and if not whether helix-helix interactionsmight stabilize their insertion. From the experimentally determined biological hydrophobicity scale, ve out of thetwelve transmembrane segments of LacY are predicted to have low spontaneous insertion, which is qualitativelyconrmed in a simplied simulation model using an implicit membrane environment as well as experimentallyin vitro. For some pairs a small, but signicant, increase in insertion eciency was seen both in the simulationsand in the in vitro system. However, the overall insertion eciency is only marginally increased when pairsof borderline hydrophobic helices are co-inserted, which suggests that translocon-mediated membrane insertionpredominantly recognizes individual helices. It also seems to imply that stabilization of marginally hydrophobichelices - at least for LacY - is a collective eect in the nal folded membrane protein, rather than caused by favorable interactions and hairpin formation during insertion.

Ämnesord

NATURVETENSKAP  -- Biologi -- Biokemi och molekylärbiologi (hsv//swe)

NATURAL SCIENCES  -- Biological Sciences -- Biochemistry and Molecular Biology (hsv//eng)

NATURVETENSKAP  -- Biologi -- Bioinformatik och systembiologi (hsv//swe)

NATURAL SCIENCES  -- Biological Sciences -- Bioinformatics and Systems Biology (hsv//eng)

Nyckelord

Membrane protein

transmembrane helix

hydrophobic

insertion

interactions

Monte Carlo

Cell and molecular biology

Cell- och molekylärbiologi

Bioinformatics

Bioinformatik

Biochemistry

biokemi

Publikations- och innehållstyp

vet (ämneskategori)

ovr (ämneskategori)