Professor Jian Lu

J.Lu@umist.ac.uk

Tel:(0)161 200 3926

UMIST Main Building, Room G13b

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Current Research Interests

My current research work is mainly focused on physical aspects of interfacial events related to lipids, proteins, peptides and therapeutic biomacromolecules. These studies utilize state-of-the-art techniques such as neutron reflection, SANS, AFM and spectroscopic ellipsometry coupled with surface specific biochemical assays. A few current research topics are outlined as follows.

(A) Protein adsorption and unfolding at interfaces

(B) Interfacial interaction between proteins and surfactants

(C) Surface biocompatibility

(D) Controlled release from PC coatings

(E) Self-assembly of small peptides

 

(A) Protein adsorption and unfolding at interfaces

Folding, unfolding and refolding of proteins in 3D space have been extensively investigated in recent years. This advance is largely due to a number of key techniques available. The techniques that are feasible for unraveling structural details characteristic of protein unfolding at wet interfaces are however limited. We have recently demonstrated that neutron reflection offers sufficiently reliable information about the structure and composition of protein molecules at interfaces. This information together with the crystalline structure of the protein enables us to assess the extent of structural deformation and in some cases unfolding leading to the complete loss of globular framework. These structural details together with complementary studies from infrared spectroscopy can provide a useful assessment of protein unfolding caused by the forces operated at interfaces, e.g., surface hydrophobicity, hydrogen bonding, lateral electrostatic repulsion.

 

Reversible

 

 

Figure 1: Lysozyme at a hydrophilic interface

              (Langmuir 1998, 14, 438-445)

80Å

 

15Å

 

Figure 2: Lysozyme at a hydrophobic interface

                 (J. Colloid Interface Sci. 1998, 206, 212-223)

As examples, we show that lysozyme retains its globular structure upon adsorption at the hydrophilic silicon oxide/solution interface (Figure 1). However, if the surface is hydrophobed, the adsorbed protein unfolds completely (Figure 2). This trend has been found for greater blood protein molecules such as HSA, IgG and fibrinogen.

(B) Interfacial interaction between proteins and surfactants

The use of SDS (sodium dodecyl sulphate) as denaturant in gel assays is an experiment familiar to biochemists, but the molecular processes of binding of surfactants to proteins at interfaces are poorly understood. This is especially so when the surfactant concentration is below its critical micellar concentration (CMC). Study of interaction between the two species at interfaces is of both fundamental and technological significance. A relevant case is the removal of blood proteins by surfactants from surfaces of a wide range of reused medical devices. Our experiments will shed light on how the extent of protein removal is affected by the chemistry of the surfaces, the type of proteins (e.g., CJD related prion proteins), and the type of surfactants. We show in Figure 3 that pre-deposited HSA on hydrophilic silicon oxide can be easily removed through formation of interfacial complexes with SDS but when cationic C12TAB is used, only partial removal is achieved.

Text Box: GProteinText Box: Gsurfactant
 

 

 

 

 

 

 

 

 

 


Figure 3: Removal profiles for HAS displaced by SDS (red) and C12TAB (blue)

(C) Surface biocompatibility

In a number of recent publications we have shown that coating of a thin film of acrylic polymers bearing pendent phosphorylcholine (PC) groups reduces protein deposition. These PC surfaces show a substantially improved biocompatibility than other polymers.  Using surface sensitive techniques such as neutron reflection we have shown that the enhanced surface biocompatibility is related to the preferential expression of PC groups on the outer film surface. We have subsequently demonstrated that coating of a self-assembled molecular monolayer with terminal PC groups equally reduces non-specific protein deposition (Figure 4). This result demonstrates that coating of an ultrathin PC film onto medical devices works just as well as thick PC films. This concept proofing has challenged traditional views on biopolymer film coatings for the improvement of surface biocompatibility and has direct economic benefit to biomedical companies such as Biocompatibles.

Figure 4: PC Containing dimer for surface compatibilisation

              (Chem. Commun. 2000, 587-588)

(D) Controlled release from PC coatings

Drug incorporated stent coating can benefit wound recovery after stent implantation for the restoration of blood flow (Figure 5). The controlled drug release can also regulate tissue re-growth thus setting controls over re-narrowing or stent restenosis. However, because the polymers used generally inhibit non-specific protein adsorption and many potentially useful drugs are proteins or plasmid DNAs by nature, it is difficult to load drugs into polymeric carriers and to control the release kinetics.  The fundamental issues related to the biomacromolecular loading and release can be conveniently performed at test tube level before further experiments are planned towards pre-clinical trials. We aim to contribute to this part of research using our extensive knowledge on proteins, polymers and biointerfaces, and the range of technical skills we have learnt from the fundamental research.

Figure 5: Action of drug containing stent

 

 (E) Self-assembly of small peptides

Many short peptides show characteristic features of aggregation and surface adsorption, as in the case of surfactants. However, the chemical structure of any peptide is more complex than amphiphilic surfactant like SDS. Although peptides such as Alzheimer peptide have a broad feature of hydrophilic and hydrophobic portions, each amino acid residue acts like a surface-active species. We are particularly interested in the structure and kinetics of adsorption and aggregation of wild and synthetic peptides with some ten amino acid residues. The use of a range of physical techniques together with established bioassays may offer new insight into the general features of self-assembly in relation to the primary and secondary structures, which may help understand the development of fibrillar deposits from soluble protofibrils.  

 

 

Last updated on 3/13/02
All comments to: I.Hopkinson@umist.ac.uk

 

 

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