Membranome 3.0: Database of single-pass membrane proteins with AlphaFold models.

The Membranome database provides comprehensive structural information on single-pass (i.e., bitopic) membrane proteins from six evolutionarily distant organisms, including protein-protein interactions, complexes, mutations, experimental structures, and models of transmembrane α-helical dimers. We present a new version of this database, Membranome 3.0, which was significantly updated by revising the set of 5,758 bitopic proteins and incorporating models generated by AlphaFold 2 in the database. The AlphaFold models were parsed into structural domains located at the different membrane sides, modified to exclude low-confidence unstructured terminal regions and signal sequences, validated through comparison with available experimental structures, and positioned with respect to membrane boundaries. Membranome 3.0 was re-developed to facilitate visualization and comparative analysis of multiple 3D structures of proteins that belong to a specified family, complex, biological pathway, or membrane type. New tools for advanced search and analysis of proteins, their interactions, complexes, and mutations were included. The database is freely accessible at https://membranome.org.

Thermodynamics-Based Molecular Modeling of α-Helices in Membranes and Micelles.

The Folding of Membrane-Associated Peptides (FMAP) method was developed for modeling α-helix formation by linear peptides in micelles and lipid bilayers. FMAP 2.0 identifies locations of α-helices in the amino acid sequence, generates their three-dimensional models in planar bilayers or spherical micelles, and estimates their thermodynamic stabilities and tilt angles, depending on temperature and pH. The method was tested for 723 peptides (926 data points) experimentally studied in different environments and for 170 single-pass transmembrane (TM) proteins with available crystal structures. FMAP 2.0 detected more than 95% of experimentally observed α-helices with an average error in helix end determination of around 2, 3, 4, and 5 residues per helix for peptides in water, micelles, bilayers, and TM proteins, respectively. Helical and nonhelical residue states were predicted with an accuracy from 0.86 to 0.96, and the Matthews correlation coefficient was from 0.64 to 0.88 depending on the environment. Experimental micelle- and membrane-binding energies and tilt angles of peptides were reproduced with a root-mean-square deviation of around 2 kcal/mol and 7°, respectively. The TM and non-TM states of hydrophobic and pH-triggered α-helical peptides in various lipid bilayers were reproduced in more than 95% of cases. The FMAP 2.0 web server (https://membranome.org/fmap) is publicly available to explore the structural polymorphism of antimicrobial, cell-penetrating, fusion, and other membrane-binding peptides, which is important for understanding the mechanisms of their biological activities.

TMPfold: A Web Tool for Predicting Stability of Transmembrane α-Helix Association.

Estimating energies of transmembrane (TM) α-helix association is essential for understanding folding of membrane proteins and formation of their functional assemblies. A new physics-based method was developed and implemented in the TMPfold web server for the calculation of the free energy of TM helix association (ΔGasc) in TM α-bundles of known structure. The method was verified using the experimental ΔGasc values for 36 TM complexes, including dimers of 10 glycophorin A mutants. The calculated free energy changes (ΔΔGasc) caused by mutations in TM helices correlated with experimental changes in the stability of 42 mutants of bacteriorhodopsin and 25 mutants of rhomboid protease. TMPfold was applied for evaluation of ΔGasc in 554 PDB structures of 85 seven-helical TM proteins and identification of stable two-helical folding intermediates. The proposed tentative paths of cotranslational helix assembly of several polytopic proteins were consistent with experimental studies of their folding. TMPfold is accessible at (https://opm.phar.umich.edu/tmpfold_server).