4 research outputs found
Structural Characterization of the Extracellular Domain of CASPR2 and Insights into Its Association with the Novel Ligand Contactin1
Contactin-associated protein-like 2 (CNTNAP2) encodes for CASPR2, a multidomain
single transmembrane protein belonging to the neurexin superfamily that has been
implicated in a broad range of human phenotypes including autism and language
impairment. Using a combination of biophysical techniques, including small angle
x-ray scattering, single particle electron microscopy, analytical
ultracentrifugation, and bio-layer interferometry, we present novel structural
and functional data that relate the architecture of the extracellular domain of
CASPR2 to a previously unknown ligand, Contactin1 (CNTN1). Structurally, CASPR2
is highly glycosylated and has an overall compact architecture. Functionally, we
show that CASPR2 associates with micromolar affinity with CNTN1 but, under the
same conditions, it does not interact with any of the other members of the
contactin family. Moreover, by using dissociated hippocampal neurons we show that
microbeads loaded with CASPR2, but not with a deletion mutant, co-localize with
transfected CNTN1, suggesting that CNTN1 is an endogenous ligand for CASPR2.
These data provide novel insights into the structure and function of CASPR2,
suggesting a complex role of CASPR2 in the nervous system
Nucleotide-free structures of KIF20A illuminate atypical mechanochemistry in this kinesin-6
KIF20A is a critical kinesin for cell division and a promising anti-cancer drug target. The mechanisms underlying its cellular roles remain elusive. Interestingly, unusual coupling between the nucleotide- and microtubule-binding sites of this kinesin-6 has been reported, but little is known about how its divergent sequence leads to atypical motility properties. We present here the first high-resolution structure of its motor domain that delineates the highly unusual structural features of this motor, including a long L6 insertion that integrates into the core of the motor domain and that drastically affects allostery and ATPase activity. Together with the high-resolution cryo-electron microscopy microtubule-bound KIF20A structure that reveals the microtubule-binding interface, we dissect the peculiarities of the KIF20A sequence that influence its mechanochemistry, leading to low motility compared to other kinesins. Structural and functional insights from the KIF20A pre-power stroke conformation highlight the role of extended insertions in shaping the motor's mechanochemical cycle. Essential for force production and processivity is the length of the neck linker in kinesins. We highlight here the role of the sequence preceding the neck linker in controlling its backward docking and show that a neck linker four times longer than that in kinesin-1 is required for the activity of this motor