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Usman A, Weatherbee SL, Collinson MM, Hohn KL, Higgins DA. Single Molecule Spectroscopy Studies of Acid-Base Chemical Gradients Using Nile Red as a Probe of Local Surface Acidity. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2021; 37:12138-12147. [PMID: 34606716 DOI: 10.1021/acs.langmuir.1c02059] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
Single molecule spectroscopy studies of local acidity along bifunctional acid-base gradients are reported. Gradients are prepared by directional vapor phase diffusion and subsequent reaction of 3-aminopropyl-trimethoxysilane with a uniform silica film. Gradient formation is confirmed by spectroscopic ellipsometry and by static water contact angle measurements. X-ray photoelectron spectroscopy is used to characterize the nitrogen content and degree of nitrogen protonation along the gradient. Nile Red is employed as the probe dye in single molecule spectroscopy studies of these gradients. While Nile Red is well-known for its solvent sensitivity, it is used here, for the first time, to sense the acid/base properties of the film in two-color wide-field fluorescence imaging experiments. The data reveal broad bimodal distributions of Nile Red emission spectra that vary along the gradient direction. The single molecule results are consistent with solution phase ensemble acid/base studies of the dye. The former reveal a gradual transition from a surface dominated by basic aminosilane sites at the high-amine end of the gradient to one dominated by acidic silanol sites at the low-amine end. The sub-diffraction-limited spatial resolution afforded by superlocalization of the single molecules reveals spatial correlations in the acid/base properties of the gradient over ∼200 nm distances. These studies provide data relevant to the use of aminosilane-modified silica in bifunctional, cooperative chemical catalysis.
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Affiliation(s)
- Abdulhafiz Usman
- Department of Chemical Engineering, Kansas State University, Manhattan, Kansas 66506, United States
| | - Shelby L Weatherbee
- Department of Chemistry, Virginia Commonwealth University, Richmond, Virginia 23284, United States
| | - Maryanne M Collinson
- Department of Chemistry, Virginia Commonwealth University, Richmond, Virginia 23284, United States
| | - Keith L Hohn
- Department of Chemical Engineering, Kansas State University, Manhattan, Kansas 66506, United States
- Department of Chemical, Paper, and Biomedical Engineering, Miami University, Oxford, Ohio 45056, United States
| | - Daniel A Higgins
- Department of Chemistry, Kansas State University, Manhattan, Kansas 66506, United States
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Liu Q, Bautista-Gomez J, Higgins DA, Yu J, Xiong Y. Dysregulation of the AP2M1 phosphorylation cycle by LRRK2 impairs endocytosis and leads to dopaminergic neurodegeneration. Sci Signal 2021; 14:14/693/eabg3555. [PMID: 34315807 DOI: 10.1126/scisignal.abg3555] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Mutations in the kinase LRRK2 and impaired endocytic trafficking are both implicated in the pathogenesis of Parkinson's disease (PD). Expression of the PD-associated LRRK2 mutant in mouse dopaminergic neurons was shown to disrupt clathrin-mediated endocytic trafficking. Here, we explored the molecular mechanism linking LRRK2 to endocytosis and found that LRRK2 bound to and phosphorylated the μ2 subunit of the adaptor protein AP2 (AP2M1), a core component of the clathrin-mediated endocytic machinery. Analysis of human SH-SY5Y cells and mouse neurons and tissues revealed that loss of LRRK2 abundance or kinase function resulted in decreased phosphorylation of AP2M1, which is required for the initial formation of clathrin-coated vesicles (CCVs). In contrast, overexpression of LRRK2 or expression of a Parkinson's disease-associated gain-of-function mutant LRRK2 (G2019S) inhibited the uncoating of AP2M1 from CCVs at later stages and prevented new cycles of CCV formation. Thus, the abundance and activity of LRRK2 must be calibrated to ensure proper endocytosis. Dysregulated phosphorylation of AP2M1 from the brain but not thyroid tissues of LRRK2 knockout and G2019S-knockin mice suggests a tissue-specific regulatory mechanism of endocytosis. Furthermore, we found that LRRK2-dependent phosphorylation of AP2M1 mediated dopaminergic neurodegeneration in a Drosophila model of PD. Together, our findings provide a mechanistic link between LRRK2, AP2, and endocytosis in the pathogenesis of PD.
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Affiliation(s)
- Qinfang Liu
- Department of Neuroscience, University of Connecticut School of Medicine, Farmington, CT 06030, USA.,Department of Anatomy and Physiology, Kansas State University College of Veterinary Medicine, Manhattan, KS 66506, USA
| | | | - Daniel A Higgins
- Department of Chemistry, Kansas State University, Manhattan, KS 66506, USA
| | - Jianzhong Yu
- Department of Anatomy and Physiology, Kansas State University College of Veterinary Medicine, Manhattan, KS 66506, USA. .,Department of Physiology and Neurobiology, University of Connecticut, Storrs, CT 06269, USA
| | - Yulan Xiong
- Department of Neuroscience, University of Connecticut School of Medicine, Farmington, CT 06030, USA. .,Department of Anatomy and Physiology, Kansas State University College of Veterinary Medicine, Manhattan, KS 66506, USA
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