Chemistry Reference
In-Depth Information
drugs are marketed that are the exclusive result of the fragment approach, the principles
can clearly be seen in the remarkable specificity and potency of recently marketed kinase
inhibitors such as imatinib and gefitinib and, indeed, many fragment-based drugs are in
the late stages of clinical trials.
[
2
]
Membrane proteins represent a similar pharmacological
challenge in that one would like to be able to address specifically individual targets from
amongst large numbers of closely related members of a protein family. However, it is
currently not possible to use the molecular methods developed for soluble proteins for drug
discovery efforts on membrane proteins.
Amajor goal of the research in our laboratory is to adapt methods developed for soluble
targets to membrane proteins or to develop alternative ones. Although we are clearly only
at the beginning stages of this process, we have nonetheless made a promising start. We
have been able to immobilize a variety of membrane proteins in functional form and have
carried out ligand screening on two. Our current efforts are geared towards finding new
ways to solubilize and immobilize membrane proteins that can be more widely applied. We
are also looking towards a variety of methods to improve the sensitivity of TINS, including
experiments that are better optimized for the diffusion-limited nature of the heterogeneous
system we employ and possible implementation of a TINS cryoprobe.
Once one finds and validates hits, it is of course necessary to evolve these towards
high-affinity, high-specificity ligands. The hit evolution process is greatly aided by the
availability of three-dimensional structural information of target-ligand complexes for sol-
uble targets. Since crystallography of membrane proteins is not yet widely applicable, it will
be imperative to develop alternative approaches. We envision a number of such approaches
that utilize the power of liquid- or solid-state NMR. In recent years, both solid-state NMR
55
and solution-state NMR
[
56
]
have made significant progress in elucidating 3D structures of
either the membrane protein itself or ligands bound to membrane proteins. Although it is
vital that these efforts continue, it is also logical that NMR should be employed to take
advantage of its unique ability to rapidly generate local, low-resolution structural informa-
tion. For this we foresee new applications in chemical shift perturbation-based modeling of
protein-ligand complexes,
[
57
]
sparse NOE-based methods
[
58, 59
]
and paramagnetic NMR.
[
60
]
With the foreseeable advancements in ligand screening and structural analysis, the era of
molecular drug discovery on membrane protein targets should soon be upon us.
6.6 Abbreviations
AMPPNP
aden-5
-yl imidodiphosphate
ATP
adenosine triphosphate
CLog
P
logarithm of the partition coefficient between
n
-octanol and water
CMC
critical micellar concentration
CTAB
cetyltrimethylammonium bromide
CTAC
cetyltrimethylammonium chloride
DHPC
dihexanoylphosphatidylcholine
DMPC
dimyristoylphosphatidylcholine
DMSO
dimethyl sulfoxide
DPC
dodecylphosphocholine
