Functional metagenomic screening identifies an unexpected β-glucuronidase.

Area of Science:

• Biochemistry
• Enzymology
• Metagenomics

Background:

• Vast amounts of protein sequence data exist, but experimental functional annotations are limited.
• Current bioinformatics tools struggle to predict the function of many enzymes.
• Metagenomic libraries offer a rich source of novel enzyme discovery.

Purpose of the Study:

• To identify novel enzymes with beta-glucuronidase activity using a functional metagenomic approach.
• To characterize the identified enzyme, SN243, including its homology, kinetics, and structure.
• To demonstrate the utility of ultrahigh-throughput screening in functional enzyme annotation.

Main Methods:

• Screening of a million-membered metagenomic library in microfluidic droplets for beta-glucuronidase activity.
• Identification and isolation of the enzyme SN243.
• Bioinformatic analysis to determine homology and enzyme family.
• Kinetic analyses and structural analysis of SN243.
• Ultrahigh-throughput screening using picolitre-volume microfluidic droplets (>10^7 library members per day).

Main Results:

• Identified SN243, a novel beta-glucuronidase belonging to the glycoside hydrolase 3 family.
• SN243 shows little homology to previously characterized enzymes of this type.
• Kinetic analysis revealed SN243 as a promiscuous catalyst.
• Structural analysis indicated unique features contributing to a wide-open active site.
• The functional metagenomic screening achieved a throughput enabling rapid functional assignments.

Conclusions:

• Functional metagenomic screening is effective for discovering enzymes with unpredictable functions.
• SN243 expands the known diversity within the glycoside hydrolase 3 family.
• Microfluidic droplet technology significantly enhances the speed and scale of functional enzyme discovery.
• This approach complements existing enzyme databases and facilitates the annotation of unexplored sequence space.