# Determining the impact of cargo membrane fluidity on motor protein function

> **NIH NIH R15** · UNIVERSITY OF CALIFORNIA, MERCED · 2024 · $460,552

## Abstract

Project Summary/Abstract
The goal of this renewal application is to determine the impact of the lipid membrane enclosing cellular cargos
on the function of the major microtubule-based motor protein kinesin-1. Motor protein-based transport underlies
all eukaryotic cell function and survival; understanding the mechanistic basis of motor protein regulation is critical
for understanding this fundamental process of intracellular transport. Our central hypothesis is that the fluid
nature of the cargo membrane is a key determinant of motor protein function. In cells, motor proteins are typically
attached to cargos via a fluid lipid membrane. This membrane is “fluid” in that its constituents, including
associated motor proteins, are mobile and diffuse on the cargo surface. Alterations in membrane fluidity are
increasingly linked to aging and neurodegeneration, in which dysfunction in motor-based transport is a common
early hallmark. Quantitative investigations of cargo membrane effects on motor function have remained limited,
with most cargos in current in vitro assays lacking a physiological lipid membrane.
Closing this major gap, in prior funding periods, the research team developed a robust optical-trapping assay to
directly measure the transport of membrane-enclosed cargos in vitro. Using this assay, the research team
demonstrated the first direct support for the central hypothesis of this project. Specifically, a fluid membrane
enhances the productive binding of kinesin to microtubules; this enhancement is countered by cholesterol, which
reduces membrane fluidity. These membrane effects were established in the presence of tau, an in vivo factor
critical for microtubule polymerization and stabilization but that occludes kinesin binding sites on microtubules.
Building on this recent work, in the next funding period the research team will test the central hypothesis by
pursuing three independent but related aims. Aim 1 will leverage the recently developed assay to test the
hypothesis that a reduction in membrane fluidity underlies the inhibitory effect of membrane cholesterol on
kinesin binding in the presence of tau. Aim 2 will extend the assay and implement high temporal resolution
detection to test the hypothesized membrane effect on kinesin binding in the absence of tau. Aim 3 will develop
a stochastic simulation model to quantitatively test the hypothesis that cargo membrane fluidity determines
kinesin-microtubule binding by impacting the diffusive search time of kinesin for open binding sites on the
microtubule.
Accomplishing the proposed project has the potential to establish cargo membrane fluidity as an unexplored
physiological determinant of kinesin-microtubule binding, advancing scientific knowledge in the mechanistic
basis of motor protein regulation, and providing a controlled experimental and computational platform for
quantitative investigations of physiological determinants of motor protein function. Findings could pave the way
for futu...

## Key facts

- **NIH application ID:** 11043724
- **Project number:** 2R15GM120682-03
- **Recipient organization:** UNIVERSITY OF CALIFORNIA, MERCED
- **Principal Investigator:** Jing Xu
- **Activity code:** R15 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2024
- **Award amount:** $460,552
- **Award type:** 2
- **Project period:** 2016-08-19 → 2027-09-29

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/11043724

## Citation

> US National Institutes of Health, RePORTER application 11043724, Determining the impact of cargo membrane fluidity on motor protein function (2R15GM120682-03). Retrieved via AI Analytics 2026-05-24 from https://api.ai-analytics.org/grant/nih/11043724. Licensed CC0.

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