The curious cell biology of prolamins and its biotechnological implications

D.ssa Emanuela Pedrazzini 
IBBA - CNR - Italy

June 24, 2026 (11:30-12:30)
Webinar Link: https://teams.microsoft.com/meet/343524945937994?p=KtWxBhr09Wd26iNrp9

Abstract: Increasing the nutritional value of seed storage proteins has been largely hindered by the limited understanding of how the features of the various seed protein domains determine high accumulation in protein storage vacuoles (PSV) or as endoplasmic reticulum-located insoluble protein bodies (PBs). The ability to form PBs is a peculiar, unique feature of cereal seed prolamins, mainly guided by their physical-chemical properties, and has no counterpart in the animal kingdom. With the aim of enhancing the nutritional quality of seed storage proteins, we created zeolin, a chimeric protein formed by the whole phaseolin (PHSL, the main storage protein of Phaseolus vulgaris, located in PSV) and the N-terminal domain of 27kD gamma-zein (27gz, a major PB prolamin in Zea mays). Zeolin has a more balanced essential amino acid composition compared to the two original proteins. When constitutively expressed in transgenic tobacco plants, zeolin forms insoluble homomeric PB very similar to those of maize seeds, indicating that the zein domain has a dominant effect over PHSL. Recently, we have determined that another maize PB prolamin (16kDa gamma-zein, 16gz), which evolved from 27gz following maize genome duplication, remains partially soluble and forms unusual structures in the ER when ectopically expressed. We now created zeolin2 (zeo2) by fusing PHSL to the N-terminal domain of 16gz. We show that zeo2 is mainly soluble, does not form PBs, and in relevant proportion traffics to vacuoles, indicating that the 16gz domain, unlike that 27gz, fails to dominate over PHSL. Moreover, zeo2 is more easily degraded during seed germination. The discovered zeo2 features could be beneficial from a nutritional point of view. Overall, these findings provide valuable insights into the role of specific protein domains in determining storage protein behavior and may support the development of tailor-made nutritionally enhanced neo-proteins. Funded by Next Generation EU PNRR, projects: M4C2I3.1 IR0000032 ITINERIS; M4C2I1.4 CN00000022 AGRITECH; PRIN2022 “PROSPER" 202255FK5F

Author's Info: https://ibba.cnr.it/staff/emanuela-pedrazzini/