Probing heat-stable water-soluble proteins from barley to malt and beer

Proteins determine the quality of barley in malting and brewing end-uses. In this regard, water-soluble barley proteins play a major role in the formation, stability, and texture of head foams. Our objective was to survey the barley seed proteins that could be involved in the foaming properties of beer. Therefore, two-dimensional (2-D) electrophoresis and mass spectrometry were combined to highlight the barley proteins that could resist the heating treatments occurring during malting and brewing processes. As expected, from barley to malt and to beer, most of the heat-stable proteins are disulfide-rich proteins, implicated in the defense of plants against their bio-aggressors, e.g., serpin-like chymotrypsin inhibitors (protein Z), amylase and amylase-protease inhibitors, and lipid transfer proteins (LTP1 and LTP2). For LTP1s, the complex pattern displayed in 2-D electrophoresis could be related to some chemical modifications already described elsewhere, such as acylation or glycation through Maillard reactions, which occur on malting. Our proteomics approach allowed the identification of the numerous proteins present in beer in addition to the major ones already described. The involvement of these proteins in the quality of beer foam can now be evaluated.

Localization of nonspecific lipid transfer proteins correlate with programmed cell death responses during endosperm degradation in Euphorbia lagascae seedlings

When the storage materials have been depleted, the endosperm cells undergo programmed cell death. Very little is known about how the components of the dying cells are recycled and used by the growing seedling. To learn more about endosperm degradation and nutrient recycling, we isolated soluble proteins from the endosperm of Euphorbia lagascae seedlings collected 2, 4, and 6 d after sowing. The protein extracts were subjected to two-dimensional gel electrophoresis. Proteins that increased in amount in the endosperm with time were selected for further analysis with mass spectrometry. We successfully identified 17 proteins, which became more abundant by time during germination. Among these proteins were three E. lagascae lipid transfer proteins (ElLTPs), ElLTP1, ElLTP2, and ElLTP3. Detailed expressional studies were performed on ElLTP1 and ElLTP2. ElLTP1 transcripts were detected in endosperm and cotyledons, whereas ElLTP2 transcripts were only detected in endosperm. Western blots confirmed that ElLTP1 and ElLTP2 accumulate during germination. Immunolocalization experiments showed that ElLTP1 was present in the vessels of the developing cotyledons, and also in the alloplastic space in the endosperm. ElLTP2 formed a concentration gradient in the endosperm, with higher amounts in the inner regions close to the cotyledons, and lesser amounts in the outer regions of the endosperm. On the basis of these data, we propose that ElLTP1 and ElLTP2 are involved in recycling of endosperm lipids, or that they act as protease inhibitors protecting the growing cotyledons from proteases released during programmed cell death.

Inhibition of proteasome activity by the TED4 protein in extracellular space: a novel mechanism for protection of living cells from injury caused by dying cells

In maturation process of tracheary element (TE) differentiation, many hydrolases are activated to execute programmed cell death of TEs. Such hydrolases are released from maturing TEs into extracellular space. The release of hydrolases should be harmful to surrounding cells. The TED4 protein, a tentative plant non-specific lipid transfer protein that is expressed preferentially in TE-induced culture of zinnia (Zinnia elegans L.), is secreted into the apoplastic space prior to and associated with morphological changes of TEs. Our studies on the interrelationship between the TED4 protein and proteolytic activities using an in vitro TE differentiation system of zinnia revealed the following facts. (1) Active proteasome is released into medium at maturation stage of TE differentiation. (2) The TED4 protein forms a complex with proteasome in culture medium. (3) The TED4 protein inhibits proteasome activity in the medium and crude extracts of zinnia cells. (4) The depletion of the TED4 protein from culture medium results in an increase in mortality of other living cells. These results strongly suggest that the secreted TED4 protein acts as an inhibitor of proteasome to protect other cells from undesirable injury due to proteolytic activities exudated from dying TEs.