[ATP-dependent proteinase La from Escherichia coli]

Area of Science:

• Biochemistry
• Molecular Biology
• Enzymology

Background:

• The ATP-dependent La proteinase (also known as Lon protease) from E. coli is a crucial enzyme involved in protein degradation.
• Previous literature suggested that Ser368 might be catalytically active, but this remained unconfirmed.

Purpose of the Study:

• To investigate the catalytic activity of specific serine residues (Ser679 and Ser368) in the E. coli La proteinase.
• To confirm the gene structure of the E. coli La proteinase and analyze controversial regions.
• To explore the functional requirements of La proteinase in vivo.

Main Methods:

• Isolation of homogeneous preparations of wild-type E. coli La proteinase and two mutant forms (Ser679Ala and Ser368Ala).
• Analysis of gene fragments to confirm the gene structure of the lon gene encoding La proteinase.
• In vitro assays to assess the catalytic activity of the isolated proteinase preparations.

Main Results:

• Ser679 was identified as the catalytically active residue in E. coli La proteinase, contradicting previous suggestions about Ser368.
• The gene structure of the E. coli La proteinase was confirmed, validating previous findings.
• La proteinase exhibited inactivity in certain in vitro systems, indicating a potential requirement for additional factors for its in vivo function.

Conclusions:

• The catalytic activity of E. coli La proteinase resides in Ser679.
• The functioning of La proteinase in vivo is likely dependent on accessory factors, suggesting a non-autonomous role.