Plant polygalacturonase structures specify enzyme dynamics and processivities to fine-tune cell wall pectins

Area of Science:

• Plant Biology
• Biochemistry
• Structural Biology

Background:

• Polygalacturonases (PGs) are crucial enzymes that modify pectin in plant cell walls, influencing development.
• The diversity and specificity of numerous plant PGs remain incompletely understood.
• Understanding PG function is key to deciphering plant cell wall dynamics.

Purpose of the Study:

• To elucidate the structural basis for the distinct activities of two Arabidopsis PGs: PGLR and ADPG2.
• To investigate the impact of PG structural variations on enzyme kinetics, processivity, and substrate hydrolysis.
• To determine the role of PG processivity in regulating root development.

Main Methods:

• X-ray crystallography to determine the structures of PGLR and ADPG2.
• Molecular dynamic simulations to analyze enzyme-substrate interactions.
• Enzyme kinetics assays and analysis of hydrolysis products to assess processivity.
• Exogenous application of purified PGs to Arabidopsis roots to study developmental effects.

Main Results:

• Crystal structures revealed amino acid variations in PGLR and ADPG2 that prevent inhibition by endogenous PG-inhibiting proteins (PGIPs).
• Distinct amino acid compositions in substrate-binding subsites led to differences in enzyme-substrate dynamics and processivity.
• ADPG2 produced shorter oligogalacturonides (DP ≤4), while PGLR produced longer ones (DP 5–9).
• ADPG2 significantly affected root cell elongation and adhesion in Arabidopsis.

Conclusions:

• Enzyme processivity is a critical factor in pectin degradation by PGs.
• Structural differences in PGs directly translate to distinct substrate hydrolysis patterns.
• PG processivity plays a significant role in regulating key aspects of plant root development, including cell elongation and adhesion.