Klotho-Related Protein KLrP: Structure and Functions.

Area of Science:

• Biochemistry
• Cell Biology
• Enzymology

Background:

• Klotho (KL) family proteins possess glycoside hydrolase (GH) motifs, but their biological roles are unclear.
• The specific function of GH motifs in KL family proteins, particularly in cellular metabolism, remains largely uncharacterized.

Purpose of the Study:

• To identify the biological function of the GH motif in KL-related protein (KLrP).
• To investigate the enzymatic activity and cellular role of KLrP in glucosylceramide metabolism.

Main Methods:

• Bioinformatics analysis to identify KL family proteins as potential neutral glucocerebrosidases (GCase).
• Biochemical assays using recombinant proteins and cell lysates to assess GCase activity.
• Crystal structure determination of KLrP and its mutant.
• Small interfering RNA (siRNA) mediated knockdown in cells to evaluate the in vivo function of KLrP.

Main Results:

• KLrP was identified as a cytosolic β-glucocerebrosidase (GCase) with neutral pH optimum and conduritol B epoxide (CBE)-insensitivity.
• Crystal structures revealed KLrP adopts a (β/α)8TIM barrel fold, employing a double-displacement mechanism typical of retaining β-glycosidases.
• Knockdown of KLrP reduced neutral GCase activity and increased cellular glucosylceramide (GlcCer) levels, indicating its role in GlcCer catabolism.
• A Gaucher disease-associated KLrP mutant (D106N) did not impair GCase activity.

Conclusions:

• KLrP is a novel cytosolic β-glucocerebrosidase involved in a previously undescribed GlcCer catabolism pathway.
• The findings provide structural insights into KLrP's enzymatic mechanism.
• The study suggests KLrP's function is distinct from its role in Gaucher disease pathogenesis, despite a specific mutation found in patients.