Ca2+and Mg2+Influence the Thermodynamics of Peptide-Membrane Interactions

Accurate quantitative estimates of protein-membrane interactions are critical to studies of membrane pro-teins. Here, we demonstrate that thermodynamic analyses based on current hydropathy scales do not account for the significant and experimentally determined effects that Ca2+ or Mg2+ have on protein -membrane interactions. We examined distinct modes of interaction (interfacial partitioning and folding and transmembrane insertion) by studying three highly divergent peptides: Bid-BH3 (derived from apop-totic regulator Bid), peripherin-2-derived prph2-CTER, and the cancer-targeting pH-Low-Insertion-Peptide (pHLIP). Fluorescence experiments demonstrate that adding 1-2 mM of divalent cations led to a substan-tially more favorable bilayer partitioning and insertion, with free energy differences of 5-15 kcal/mol.CO 2022 Elsevier Ltd. All rights reserved.