Title : Crystal structure and autoactivation pathway of the precursor form of human
tripeptidyl-peptidase 1 , the
enzyme deficient in late infantile ceroid lipofuscinosis
Abstract :
- Late infantile neuronal ceroid lipofuscinosis is a fatal childhood neurological disorder caused by a deficiency in the lysosomal protease tripeptidyl-peptidase 1 ( TPP1 )
- TPP1 represents the only known mammalian member of the S53 family of serine proteases, a group characterized by a subtilisin-like fold, a Ser-Glu-Asp catalytic triad, and an acidic pH optimum
- TPP1 is synthesized as an inactive proenzyme ( pro- TPP1 ) that is proteolytically processed into the active enzyme after exposure to low pH in vitro or targeting to the lysosome in vivo
- In this study, we describe an endoglycosidase H-deglycosylated form of TPP1 containing four Asn-linked N-acetylglucosamines that is indistinguishable from fully glycosylated TPP1 in terms of autocatalytic processing of the proform and enzymatic properties of the mature protease
- The crystal structure of deglycosylated pro- TPP1 was determined at 1.85 angstroms resolution
- A large 151-residue C-shaped prodomain makes extensive contacts as it wraps around the surface of the catalytic domain with the two domains connected by a 24-residue flexible linker that passes through the substrate-binding groove
- The proenzyme structure reveals suboptimal catalytic triad geometry with its propiece linker partially blocking the substrate-binding site , which together serve to prevent premature activation of the protease
- Finally, we have identified numerous processing intermediates and propose a structural model that explains the pathway for TPP1 activation in vitro
- These data provide new insights into TPP1 function and represent a valuable resource for constructing improved TPP1 variants for treatment of late infantile neuronal ceroid lipofuscinosis