Biomedical Engineering Reference
In-Depth Information
22.6 EngineeringStrategiesinBSSCs
Clearly,. one. of. the. greatest. challenges. in. BSSCs,. or. in. any. future. biohybrid. technology.
endeavor,. will. be. to. preserve. the. function. of. the. integrated. proteins.. Strategies. toward.
reaching.this.goal.now.involve.an.eclectic.range.of.disciplines,.including.genetic.engineer-
ing,.colloid.science,.and.surface.chemistry.
Integrating.photosynthetic.proteins.poses.a.particularly.dificult.challenge,.as.they.are.
intramembraneous. biomolecules.. With. large. hydrophobic,. alpha. helix. structures,. these.
proteins.are.found.embedded.in.the.similarly.solvophobic.environment.within.the.cells'.
lipid.bilayers..The.complex.photosystems.extracted.from.higher.plant.forms.are.especially.
delicate.
22.6.1 Protein Engineering: Genetic Modification
However,. photoactive. proteins. from. bacteria. such. as. bacterial. reaction. centers. (RCs). or.
bacteriorhodopsin. (bR). extracted. from.
Rhodobacter sphaeroides
and.
Halobacterium salinar-
ium
,
respectively,.are.robust.and.remain.functional.out.of.their.native.environments..bR.is.
particularly.resilient.at.high.temperatures.and.extreme.pH.levels..This.may.be.attributed.
to.the.harsh.environmental.conditions.the.
Halobacterium salinarium
.have.evolved.to.thrive.
in,. resulting. in. a. relatively. simple. proton-pumping. structure.. Because. of. its. long-term.
resistance.to.photo,.thermal,.and.chemical.degradation,.bR.is.commonly.of.interest.as.a.
component.in.technical.applications.
Enhancement. of. thermostability. of. bR. has. been. an. area. of. intense. research. in. our.
laboratory..One.method.of.choice.has.been.rational.site-directed.protein.engineering.of.
bR..Advancements.in.thermostable.vectors,.antibiotic.resistance.genes,.and.the.genetic.
characterization. of. extreme. thermophiles. have. prompted. the. development. of. in. vivo.
thermoselection. systems. to. optimize. mesophilic. protein. bR. for. device. applications..
Thermus thermophilus
has. been. a. useful. in. vivo
screening. platform. for. bR. mutants;. a.
versatile,. heat-stable. expression. vector. is. required.. Others. have. constructed. a. bifunc-
tional. vector. system. (pMKE1). capable. of. expression. in. both. extremely. thermophilic.
(
T. thermophilus
). and. mesophilic. (
E. coli
). microorganisms.. Mutants. that. retain. struc-
tural.stability.at.elevated.temperatures.have.been.used.as.starting.points.for.additional.
rounds.of.mutagenesis.and.thermoselection..Several.iterations.of.thermoselection.may.
be.required.before.a.bR.variant.with.adequate.thermostability.suitable.for.device.appli-
cation.can.be.identiied.
Thavasi.et.al.
50.
also.studied.wild.bR.and.its.modiication.(3Glu).as.an.assembly.on.the.
TiO
2
.surface..The.modiications.were.done.by.eliminating.three.negatively.charged.Glu.
residues.. It. was. found. that. this. modiication. of. the. protein. improved. performance. of.
the. solar. cells.. Thavasi's
50
. group. also. observed. that. both. the. wild. bR. and. the. 3Glu. bR.
responded. to. light. illumination,. but. the. triple. mutant. (3Glu). gave. better. photoelectric.
performance..The.cells.assembled.with.the.triple.mutant.showed.0.038.mA/cm
2
.of.short-
circuit.photocurrent.density.(
J
SC
),.while.only.0.0269.mA/cm
2
.was.achieved.with.the.wild.
bR.. This. improved. cell. performance. was. attributed. to. the. more. eficient. assembly. and.
binding.nature.of.the.mutated.protein.(3Glu).to.TiO
2
..It.was.found.that.the.elimination.
of.the.three.negative.charges.from.the.extracellular.(EC).site.of.the.bR.structure.resulted.
in.a.dramatic.change.of.the.surface.potential.map.of.the.protein.that.could.facilitate.its.
better.binding.to.TiO
2
.
