The human immunodeficiency virus antigen Nef forms protein bodies in leaves of transgenic tobacco when fused to zeolin.
Protein bodies (PB) are stable polymers naturally formed by certain seed storage proteins within the endoplasmic reticulum (ER). The human immunodeficiency virus negative factor (Nef) protein, a potential antigen for the development of an anti-viral vaccine, is highly unstable when introduced into the plant secretory pathway, probably because of folding defects in the ER environment. The aim of this study was to promote the formation of Nef-containing PB in tobacco (Nicotiana tabacum) leaves by fusing the Nef sequence to the N-terminal domains of the maize storage protein gamma-zein or to the chimeric protein zeolin (which efficiently forms PB and is composed of the vacuolar storage protein phaseolin fused to the N-terminal domains of gamma-zein). Protein blots and pulse-chase indicate that fusions between Nef and the same gamma-zein domains present in zeolin are degraded by ER quality control. Consistently, a mutated zeolin, in which wild-type phaseolin was substituted with a defective version known to be degraded by ER quality control, is unstable in plant cells. Fusion of Nef to the entire zeolin sequence instead allows the formation of PB detectable by electron microscopy and subcellular fractionation, leading to zeolin-Nef accumulation higher than 1% of total soluble protein, consistently reproduced in independent transgenic plants. It is concluded that zeolin, but not its gamma-zein portion, has a positive dominant effect over ER quality control degradation. These results provide insights into the requirements for PB formation and avoidance of quality-control degradation, and indicate a strategy for enhancing foreign protein accumulation in plants.
Istituto di Biologia e Biotecnologia Agraria, Consiglio Nazionale delle Ricerche, via Bassini 15, 20133 Milano, Italy, EU.
Maddalena
M
de Virgilio
Francesca
F
De Marchis
Michele
M
Bellucci
Davide
D
Mainieri
Marika
M
Rossi
Eugenio
E
Benvenuto
Sergio
S
Arcioni
Alessandro
A
Vitale
D000595:Amino Acid Sequence; D000956:Antigens, Viral / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D015870:Gene Expression; D006801:Humans; D002479:Inclusion Bodies / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D018515:Plant Leaves / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D030821:Plants, Genetically Modified / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D015202:Protein Engineering; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D014026:Nicotiana / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D003313:Zea mays / Q000235:genetics; D015028:Zein / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D054311:nef Gene Products, Human Immunodeficiency Virus / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
D000956:Antigens, Viral; D011993:Recombinant Fusion Proteins; D054311:nef Gene Products, Human Immunodeficiency Virus; C514837:nef protein, Human immunodeficiency virus 1; D015028:Zein