The Arabidopsis B3 domain protein VERNALIZATION1 (VRN1) is involved in processes essential for development, with structural and mutational studies revealing its DNA-binding surface.

The B3 DNA-binding domain is a plant-specific domain found throughout the plant kingdom from the alga Chlamydomonas to grasses and flowering plants. Over 100 B3 domain-containing proteins are found in the model plant Arabidopsis thaliana, and one of these is critical for accelerating flowering in response to prolonged cold treatment, an epigenetic process called vernalization. Despite the specific phenotype of genetic vrn1 mutants, the VERNALIZATION1 (VRN1) protein localizes throughout the nucleus and shows sequence-nonspecific binding in vitro.

Cyclic peptides arising by evolutionary parallelism via asparaginyl-endopeptidase-mediated biosynthesis.

The cyclic miniprotein Momordica cochinchinensis Trypsin Inhibitor II (MCoTI-II) (34 amino acids) is a potent trypsin inhibitor (TI) and a favored scaffold for drug design. We have cloned the corresponding genes and determined that each precursor protein contains a tandem series of cyclic TIs terminating with the more commonly known, and potentially ancestral, acyclic TI. Expression of the precursor protein in Arabidopsis thaliana showed that production of the cyclic TIs, but not the terminal acyclic TI, depends on asparaginyl endopeptidase (AEP) for maturation.

Albumins and their processing machinery are hijacked for cyclic peptides in sunflower.

The cyclic peptide sunflower trypsin inhibitor 1 (SFTI-1) blocks trypsin and is a promising drug lead and protein engineering scaffold. We show that SFTI-1 and the newfound SFT-L1 are buried within PawS1 and PawS2, precursors for seed storage protein albumins. Proalbumins are matured by asparaginyl endopeptidase, which we show is required to liberate both ends of SFTI-1 as well as to mature PawS1 albumin.