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Professor Jian LuTel:(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 (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.
Figure 3: Removal profiles for HAS displaced
by SDS (red) and C12TAB (blue) 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. | |||||||||||
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Last
updated on 3/13/02
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comments to: I.Hopkinson@umist.ac.uk
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