Structure of chlorophyll synthase in complex with the LHC-like protein HliD.

Cryo-EM structures of a substrate-free and geranylgeranyl-pyrophosphate-bound ChlG 2 HliD 2 complex from Synechocystis sp. PCC 6803 reveal how HliD positions ChlG for chlorophyllide catalysis.

• Why it matters: The catalytic mechanism of the transmembrane chlorophyll synthase ChlG and the functional role of its LHC-like partner HliD are unclear, limiting understanding of chlorophyll a production.
• What they did: The authors used cryogenic electron microscopy to determine ChlG 2 HliD 2 structures in two biochemical states, complemented by AlphaFold modeling of chlorophyllide binding, plus site-directed mutagenesis and molecular dynamics simulations.
• The result: The data support proposed mechanisms for ChlG substrate specificity and catalysis, show how a central HliD homodimer binds two ChlG monomers, and define pigment arrangements that inform evolution of eukaryotic LHC antennae.

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