Functional diversification within the heme-binding split-barrel family

Area of Science:

• Biochemistry
• Molecular Biology
• Structural Biology

Background:

• Proteins with similar structures can evolve distinct functions through neofunctionalization after gene duplication.
• Sequence similarity alone is insufficient for functional annotation of divergent homologous proteins.
• Heme metabolism is crucial in various organisms, involving both enzymatic degradation and nonenzymatic sensing.

Purpose of the Study:

• To identify and characterize a multifunctional protein family involved in heme metabolism.
• To elucidate the evolutionary and functional diversity of the homolog of HugZ (HOZ) family.
• To understand the sequence-structure-function relationships of heme-binding proteins across different lineages.

Main Methods:

• Bioinformatic analysis to identify the HOZ family within the FMN-binding split barrel superfamily.
• Targeted experimentation including in vitro heme degradation assays.
• Genetic disruption experiments in Arabidopsis thaliana and structural characterization of Populus trichocarpa homologs.

Main Results:

• A large, multifunctional HOZ protein family was identified across prokaryotes, plants, and algae, binding heme and participating in its metabolism.
• Prokaryotic HOZ proteins are linked to iron assimilation; plant and algal HOZ proteins are involved in heme degradation or biosynthesis regulation.
• Disruption of HOZ1 and HOZ2 in Arabidopsis thaliana led to developmental delays, indicating essential plastid roles. A cytosolic paralog in Populus trichocarpa retained conserved heme-binding sites.

Conclusions:

• This study unifies the understanding of sequence-structure-function relationships within the multilineage HOZ family.
• New molecular players in plant and bacterial heme metabolism have been identified.
• The HOZ family represents a significant component of heme management across diverse life forms.