Purification, Characterization, and Gene Expression of Rice Endo-β-N-Acetylglucosaminidase, Endo-Os

Area of Science:

• Biochemistry
• Plant Molecular Biology

Background:

• Endoplasmic reticulum-associated degradation (ERAD) involves deglycosylation of misfolded glycoproteins.
• High-mannose type free N-glycans (HMT-FNGs) are generated by cytosolic peptide:N-glycanase (cPNGase) and endo-β-N-acetylglucosaminidase (endo-β-GlcNAc-ase).
• The physiological roles of HMT-FNGs and the characterization of these deglycosylation enzymes in plants require further investigation.

Purpose of the Study:

• To comprehensively characterize the rice endo-β-N-acetylglucosaminidase (Endo-Os), including its purification, enzymatic properties, amino acid sequence, and gene cloning.
• To elucidate the role of Endo-Os in the production of HMT-FNGs within the plant cytosol.

Main Methods:

• Purification and characterization of native Endo-Os.
• Analysis of substrate specificity and optimal pH.
• Mass spectrometry for internal amino acid sequencing.
• Gene cloning and recombinant protein expression in *Escherichia coli*.
• Comparison of enzymatic properties between native and recombinant Endo-Os.

Main Results:

• Purified Endo-Os exhibits optimal activity at pH 6.5.
• Endo-Os demonstrates high activity towards high-mannose type N-glycans with a specific mannose linkage (Manα1-2Manα1-3Manβ1).
• Mass spectrometry confirmed 17 internal amino acid sequences, consistent with the deduced sequence from cDNA clone AK112067 (gene ID: *Os05g0346500*).
• Recombinant Endo-Os expressed in *E. coli* displayed identical enzymatic properties to the native enzyme.

Conclusions:

• Endo-Os plays a critical role in the cytosolic production of HMT-FNGs in rice.
• The substrate specificity of Endo-Os is similar to other plant endo-β-GlcNAc-ases, highlighting conserved functions.
• Detailed characterization of Endo-Os provides a foundation for understanding its physiological significance in plant growth and development.