Figure 4.

A common Rubisco-binding motif mediates the assembly of the major compartments of the pyrenoid. A) In Chlamydomonas, many pyrenoid-localized proteins contain at least one Rubisco-binding motif. B) The Rubisco-binding motif mediates the assembly of the three pyrenoid sub-compartments. The motifs on EPYC1 link Rubisco to form the pyrenoid matrix (He et al. 2020). The motifs on the tubule-localized transmembrane proteins RBMP1 and RBMP2 are proposed to connect the Rubisco to the tubules, and the motifs on the putative starch-binding proteins SAGA1 and SAGA2 are proposed to mediate interactions between the matrix and the surrounding starch sheath. A Rubisco-binding motif was also shown to be necessary and sufficient to target a nascent protein to the pyrenoid (Meyer et al. 2020b). C) A model illustrating how EPYC1 (red) clusters Rubisco (blue) in the pyrenoid matrix. D) The Rubisco-binding motif of EPYC1 (red) binds to the Rubisco small subunit (dark blue) (He et al. 2020); other Rubisco-binding motifs in Chlamydomonas are expected to bind to the same site. E) The motif binds between two alpha-helices of the Rubisco small subunit.