Structural determinants of raft partitioning for single-pass transmembrane proteins and their effects on subcellular localization.
(2017) American Society of Cell Biology eeting — Location: Philadelphia
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- Abstract
- Eukaryotic plasma membranes (PMs) are compartmentalized into functional lateral domains, including lipid-driven membrane rafts. Rafts are involved in most PM functions by selective recruitment and retention of specific proteins. Transmembrane proteins (TMPs) reflect ~30% of the mammalian proteome and mediate almost all cellular functions. However, neither the structural determinants of TMP partitioning to raft domains, nor the functional consequences thereof, are known. We hypothesized that structural features of the transmembrane domain (TMD) of single-pass TMPs would guide raft partitioning and raft-dependent functionality. To explore TMD-dependent raft partitioning, we isolated intact cellular plasma membranes as Giant Plasma Membrane Vesicles (GPMVs), a model system that allows direct observation of protein partitioning between raft and non-raft domains by fluorescence microscopy. We quantified raft partitioning of >100 TMPs and identified three physical features – TMD surface area, length, and palmitoylation – that independently affect raft partitioning. Specifically, palmitoylated and longer TMDs with smaller surface areas partitioned efficiently to the more ordered raft domains. These findings were rationalized with a mechanistic, physical model wherein raft affinity is determined by the interfacial energy between a protein TMD and the surrounding lipid matrix. This model was shown to be capable of correctly predicting raft affinity solely from protein sequence. Using bioinformatics, we generated proteome-wide predictions of raft affinity and observed that PM proteins have higher predicted raft affinity than those of intracellular membranes, consistent with raft-mediated PM sorting. These predictions were confirmed by cellular experiments in which PM localization was dependent on raft affinity for a variety of unrelated TMPs. Thus, our experimental observations and physical model establish general rules for raft partitioning of TMDs and support the central role of rafts in membrane traffic.
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Lorent, J., Ilya Levental, Barbara Diaz-Rohrer, & Kandice Levental. (2017). Structural determinants of raft partitioning for single-pass transmembrane proteins and their effects on subcellular localization. Molecular Biology of the Cell, 28(26), 3727. https://doi.org/10.1091/mbc.E17-10-0618 (Original work published 2017)