Theinus communis2S albumin precursor: A single preproprotein may be processed into two different heterodimeric storage proteins

Abstract

The Ricinus communis (castor bean) 2S albumin is a heterodimer of glutamine-rich, disulphide-linked 4 and 7 kDa polypeptide. A cDNA library was constructed using mRNA from maturing castor bean endosperm as template. Clones containing sequences complementary to albumin mRNA were isolated by hybridization using as a probe a mixture of synthetic oligonucleotides representing sequences predicted for a peptide present in the 2S albumin large subunit. The nucleotide sequence contained an open reading frame encoding a preproprotein of 258 amino acid residues. The preproprotein included both polypeptides of the previously sequenced 2S albumin. In addition, this precursor included two further glutamine-rich sequences which, in term of their size and conserved cystein residues typically found in seed proteins of the 2S albumin superfamily, possible represent the small and large polypeptide subunits of a second heterodimeric storage protein. A post-translational processing scheme is proposed which would result in a single preproprotein generating two distinct heterodimeric 2S albumins. The generation of a second heterodimer seems likely since polypeptide candidates for its small and large subunits were found in the Ricinus 2S albumin fraction, and N-terminal protein sequencing confirmed the existence of the putative small subunit.

Sequence‐specific, Golgi‐dependent vacuolar targeting of castor bean 2S albumin

“…The castor bean 2S albumin precursor is translated as a single pre-proprotein that can be processed into two different heterodimeric storage proteins upon transport and delivery into the protein storage vacuoles (PSV) of castor bean endosperm (Irwin et al, 1990). Pre-proalbumin is converted to proalbumin by removal of an N-terminal signal peptide in the endoplasmic reticulum (ER) lumen, and is then traf®cked to the PSV, reportedly by a unique transport pathway that involves the packaging of proalbumin into large vesicles that bud directly from the ER and that subsequently fuse with the PSV (Hara-Nishimura et al, 1998).…”

“…Pre-proalbumin is converted to proalbumin by removal of an N-terminal signal peptide in the endoplasmic reticulum (ER) lumen, and is then traf®cked to the PSV, reportedly by a unique transport pathway that involves the packaging of proalbumin into large vesicles that bud directly from the ER and that subsequently fuse with the PSV (Hara-Nishimura et al, 1998). Arrival in the vacuole is accompanied by cleavage of three propeptides: one at the N-terminus, one from within the ®rst heterodimer, and one from within the second heterodimer together with a cleavage between the two heterodimers (Irwin et al, 1990). In comparison with other members of the albumin family, the castor bean 2S albumin is unique both in its greater size and in generating two distinct heterodimers instead of one.…”

Cotton Mat5-A (C164) Gene and Mat5-D cDNAs Encoding Methionine-Rich 2S Albumin Storage Proteins

“…In this region the sequence of MatS-A has some similarities with those of other 2S albumin storage proteins, in particular two elements (double underlined in Fig. 1) present in similar locations in many of these genes (8,9). Other elements suggested to be important in various storage protein genes (5) are not obvious in Mat5-A.…”

“…It is 10% in cotton and 19% in Bertholletia, compared with 2 to 3% in other 2S albumins (1,8,9). Four ofthe 10 methionine residues in the cotton protein are at novel positions that may be sites at which other 2S albumins could be engineered for higher methionine content.…”

Seed storage albumins: biosynthesis, trafficking and structures

“…CysV and CysVI are also highly conserved and flank a single residue whereas CysVII and CysVIII vary in their position and may be separated by 3-7 residues. Although (Rundqvist et al 2012) (a) (b) (Irwin et al 1990;Alcocer et al 2002;Pantoja-Uceda et al 2004a). The structures include a recombinant Brassica napus albumin (rproBnIb) that differs from the native BnIb protein by three residues (black) that join the small and large albumin subunit.…”