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author:("Cai, guang")
1.  Atomic Force Microscopy Study of Conformational Change of Immobilized Calmodulin 
Maintaining the biological functionality of immobilized proteins is the key to the success of numerous protein-based biomedical devices. To that end, we studied conformational change of calmodulin (CaM) immobilized on chemical patterns. 1-cysteine mutated calmodulin was immobilized on a mercapto-terminated surface through the cysteine-Hg-mercapto coupling. Utilizing Atomic Force Microscope (AFM), the average height of the immobilized calmodulin was determined to be 1.87 ± 0.19 nm. After incubation in EGTA solution, the average height of protein changed to 2.26 ± 0.21 nm, indicating conformational change of CaM to Apo-CaM. The immobilized CaM also demonstrated conformational change upon the reaction with known calmodulin antagonist chlorpromazine (CPZ). After incubation in CPZ solution, the average height of CPZ-bound CaM increased to 2.32 ± 0.20 nm, demonstrating the immobilized CaM still has the similar response as in bulk solution. These results show that immobilization of calmodulin on a solid support does not interfere with the ability of the protein to bind calcium and calmodulin antagonists. Our results demonstrate the feasibility of employing AFM to probe and understand protein conformational changes.
PMCID: PMC3164926  PMID: 21766850
calmodulin; protein conformation change; AFM
2.  Octadecyltrichlorosilane (OTS)-coated ionic liquid drops: Micro-reactors for homogenous catalytic reactions at designated interfaces 
An ionic liquid (IL), 1-butyl-3-methylimidazolium chloride ([Bmim]Cl) can assemble on prefabricated carboxylic acid–terminated chemical patterns on octadecyltrichlorosilane (OTS) film. The chemical pattern controls the position, shape and size of the IL on the surface. After the IL assembly – by incubating IL drops assembled on sample surface in an OTS silane vapor – an OTS layer was coated on the IL drop surface which encapsulated the IL drop. The OTS-coated capsule can exist stably under aqueous solution. The OTS coating protected the IL drops from being instantaneously dissolved by other solutions. We found that a homogenous catalyst (FeCl3) dissolved in [Bmim]Cl can be assembled together on the chemical patterns and subsequently encapsulated together with [Bmim]Cl by OTS coating. The pinhole defects within the vapor-coated silane layer provide space for the catalyst inside the capsule and reactants outside the capsule to meet and react. When the OTS-coated capsule containing a FeCl3/IL mixture was soaked under H2O2 solution, the Fe3+ ions catalyzed the decomposition reaction of hydrogen peroxide at the vapor-coated OTS-water interface. Since the shape and position of the interface is defined by the underneath chemical pattern, our findings show that the OTS-coated IL drops assembled on chemical patterns can be used as novel micro-reactors. This allows homogenous catalytic reactions to occur at the designated interfaces.
PMCID: PMC3304328  PMID: 22428094
AFM; catalyst encapsulation; chemical pattern; ionic liquid; OTS

Results 1-2 (2)