Protein kinase I of Mycobacterium tuberculosis: cellular localization and expression during infection of macrophage-like cells

Area of Science:

• Microbiology
• Molecular Biology
• Biochemistry

Background:

• Mycobacterium tuberculosis possesses numerous protein kinases, including PknA and PknB, which are crucial for its survival.
• The specific roles and localization of other protein kinases, such as PknI, remain less understood.
• PknI has a unique amino acid composition in its catalytic loop.

Purpose of the Study:

• To characterize the biochemical activity and sub-cellular localization of Protein kinase I (PknI) from Mycobacterium tuberculosis.
• To investigate the expression pattern of PknI during host-pathogen interaction within human macrophages.
• To differentiate PknI from other well-studied M. tuberculosis protein kinases like PknA and PknB.

Main Methods:

• Autophosphorylation and transphosphorylation assays were performed to determine PknI's enzymatic activity.
• Immunoblot analysis using anti-PknI antibodies was employed to ascertain its sub-cellular localization.
• Quantitative reverse transcription PCR (RT-PCR) combined with molecular beacons was used to measure pknI gene expression.

Main Results:

• PknI demonstrated both autophosphorylation and transphosphorylation capabilities.
• Immunoblotting confirmed PknI's localization within the bacterial cytosol, contrasting with the membrane-bound PknA.
• Relative pknI expression significantly decreased during the infection of THP-1 human macrophages, while pknA and pknB expression increased.

Conclusions:

• PknI is a functionally active protein kinase in Mycobacterium tuberculosis, distinct from PknA and PknB.
• PknI's cytosolic localization and its differential expression during macrophage infection suggest a unique role in the pathogen's lifecycle.
• These findings highlight PknI as a potential target for novel anti-tubercular therapies.