Structural biological studies of the soluble and membrane regions of KCC2

Imbalances in excitatory versus inhibitory postsynaptic signaling in the central nervous system (CNS) have been associated with autism spectrum disorders (ASD). These imbalances are caused by mis-regulated chloride (Cl–) concentrations in the CNS. The potassium-chloride co-transporter KCC2 is the key player involved in maintaining the low Cl– concentrations in neurons necessary for proper signaling. KCC2 is thus a potential target for therapeutic strategies aimed at rescuing excitatory/inhibitory imbalances in ASD and other disorders affected by such imbalances. However, targeted therapeutic strategies require detailed knowledge of the drug targets, and currently, there is insufficient biochemical information to target KCC2 using rational approaches.

The laboratories at the New York Structural Biology Center (NYSBC) overseen by David Hirsh and Jonah Cheung have expertise in the production and characterization of atomic resolution protein structures using an array of techniques, including X-ray crystallography and electron microscopy1,2. The laboratories plan to use a multipronged approach to determine atomic resolution structures of KCC2 domains – both soluble and membrane regions – that will allow them to observe both unique features (such as regions known to be required for regulation) as well as features conserved across a larger family of Cl– transporters that can reveal details of the Cl– transport mechanism. Such work has not been possible previously because protocols for the production of purified KCC2 (or any of its close homologs) had not been established.

Once high-resolution structures have been determined, NYSBC will use this information, in combination with additional biochemical assessments, to establish molecular mechanisms for KCC2 function and regulation. The results of this proposed work will provide essential insight into the molecular mechanisms of Cl– export by the KCC2 transporter. Further, establishing protocols for the purification of KCC2 will facilitate the design of molecules that alter KCC2 function using standard techniques, such as ligand-binding assays or in vitro transport assays. This will allow for the rational manipulation of KCC2 function, bringing the field closer to determining whether altering Cl– levels and restoring excitatory/ inhibitory balance in the CNS can alleviate symptoms in ASD.