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Membrane binding of MARCKS-related protein studied by tryptophan fluorescence spectroscopy
A A Schmitz1, A Ulrich, G Vergères
1Department of Biophysical Chemistry, Biozentrum of the University of Basel, Klingelbergstrasse 70, Basel, CH-4056, Switzerland.
Abstract:
MARCKS-related protein (MRP) is a peripheral membrane protein whose binding to membranes is mediated by the N-terminal myristoyl moiety and a central, highly basic effector domain. MRP mediates cross-talk between protein kinase C and calmodulin and is thought to link the actin cytoskeleton to the plasma membrane. Since MRP contains no tryptophan residues, we mutated a phenylalanine in the effector domain to tryptophan (MRP F93W) and used fluorescence spectroscopy to monitor binding of the protein to phospholipid vesicles. We report in detail the evaluation procedure necessary to extract quantitative information from the raw data. The spectra of MRP F93W obtained in the presence of increasing amounts of lipid crossed at an isosbestic point, indicating a simple transition between two states: free and membrane-bound protein. The change in fluorescence toward values typical of a more hydrophobic environment was used to quantify membrane binding. The partition coefficient agreed well with values obtained previously by other methods. To study the interaction of the N-terminus of MRP with membranes, a tryptophan residue was also introduced at position 4 (MRP S4W). Our data suggest that only the myristoylated N-terminus interacted with liposomes. These results demonstrate the versatility of site-directed incorporation of tryptophan residues to study protein-membrane interactions.
Insights
MARCKS-related protein (MRP) membrane binding was studied using fluorescence spectroscopy. Introducing tryptophan revealed that the myristoylated N-terminus drives interactions with lipid membranes.
Area of Science:
- Biochemistry
- Molecular Biology
- Biophysics
Background:
- MARCKS-related protein (MRP) is a peripheral membrane protein.
- MRP links the actin cytoskeleton to the plasma membrane and mediates signaling pathways.
- Understanding MRP's membrane interaction is crucial for cellular processes.
Purpose of the Study:
- To investigate the membrane binding mechanism of MRP using site-directed tryptophan incorporation.
- To quantify the binding affinity of MRP to phospholipid vesicles.
- To determine which part of MRP (N-terminus vs. effector domain) interacts with membranes.
Main Methods:
- Site-directed mutagenesis to introduce tryptophan residues into MRP (MRP F93W and MRP S4W).
- Fluorescence spectroscopy to monitor protein-membrane interactions.
- Quantitative analysis of spectral changes to determine partition coefficients.
Main Results:
- Fluorescence spectra of MRP F93W showed a clear transition between free and membrane-bound states, indicating successful monitoring of binding.
- The partition coefficient determined by fluorescence spectroscopy agreed with previous methods.
- Data from MRP S4W suggest that only the myristoylated N-terminus of MRP interacts with liposomes.
Conclusions:
- Site-directed tryptophan incorporation is a versatile method for studying protein-membrane interactions.
- The myristoylated N-terminus is the primary site of interaction between MRP and membranes.
- This study provides quantitative insights into the molecular mechanisms of MRP membrane association.