Photosynthesis takes place in specialized membrane systems, made up of stacked disks linked together by unstacked planar leaflets. A team of Ludwig-Maximilians-Universitaet (LMU) in Munich has now identified a protein that tucks the membrane in at the edge of each stack.
Scanning electron microscopy (SEM) micrograph of a chloroplast in maize (Zea mays) showing thylakoids (green) and assimilation starch granules (grey). (Prepared by freeze fracturing; micrograph is pseudo-colored.) (Source: G. Wanner LMU)
By making use of sunlight to generate molecular oxygen and other energy-rich chemical compounds that other organisms can utilize as nutrients, photosynthesis provides the basis for almost all life on Earth. Radiant energy from the Sun is captured by pigment-protein complexes embedded in specialized membrane systems called thylakoids. The thylakoids of green plants reside within organelles called chloroplasts, membrane-bounded compartments in the cell cytoplasm that serve as self-contained reaction vessels.
Thylakoids are made of stacks of 5 to 20 flat membrane sacs called grana, and extended planar membrane sheets that serve to interconnect them, so that all thylakoids in a chloroplast form a continuous network. To form the stacks of appressed sacs, the membrane must be bent into a tight fold at their edges. This implies that the thylakoid membranes forming the grana stacks must somehow be induced to curve at regular intervals. "The origin of the stacked organization of the thylakoids and the local alterations in membrane curvature has been a complete mystery up to now," says LMU biologist Professor Dario Leister.
Leaning into the curve with CURT1
Leister and his group have now identified a new family of proteins, whose members spontaneously cause membranes to bend. The researchers call them CURT1 proteins (for CURvature of Thylakoids). "Without CURT1 proteins, there are no stacks," Leister reports. Usi
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