Proteomic analysis of the pyrenoid-traversing membranes of Chlamydomonas reinhardtii reveals novel tubule components

Abstract

Many photosynthetic algae rely upon a unique CO2-concentrating organelle known as the pyrenoid for growth under ambient air conditions. Pyrenoids are responsible for approximately one-third of global carbon fixation, and hold the potential to enhance crop growth if they can be understood and engineered into land plants. Most pyrenoid-based CO2-concentrating mechanisms (CCMs) rely on delivery of CO2 to the carbon-fixing enzyme Rubisco by a system of membranes, often in the form of tubules connected to the photosynthetic thylakoids. Despite the critical nature of these tubules for pyrenoid function, few protein components of these tubules are known in any species. Here we adapt an affinity purification protocol to isolate intact membranes from the model alga Chlamydomonas reinhardtii and identify two novel components of the tubule membranes, LCI16 and PME1. We determine that these proteins do not play a role in shaping tubule membranes under typical CCM-inducing growth conditions, but that LCI16 physically interacts with PME1 and with the known tubule protein RBMP2.