Structure and Function of a Mitochondrial Late Embryogenesis Abundant Protein Are Revealed by Desiccation

Abstract

Few organisms are able to withstand desiccation stress; however, desiccation tolerance is widespread among plant seeds. Survival without water relies on an array of mechanisms, including the accumulation of stress proteins such as the late embryogenesis abundant (LEA) proteins. These hydrophilic proteins are prominent in plant seeds but also found in desiccation-tolerant organisms. In spite of many theories and observations, LEA protein function remains unclear. Here, we show that LEAM, a mitochondrial LEA protein expressed in seeds, is a natively unfolded protein, which reversibly folds into a-helices upon desiccation. Structural modeling revealed an analogy with class A amphipathic helices of apolipoproteins that coat low-density lipoprotein particles in mammals. LEAM appears spontaneously modified by deamidation and oxidation of several residues that contribute to its structural features. LEAM interacts with membranes in the dry state and protects liposomes subjected to drying. The overall results provide strong evidence that LEAM protects the inner mitochondrial membrane during desiccation. According to sequence analyses of several homologous proteins from various desiccationtolerant organisms, a similar protection mechanism likely acts with other types of cellular membranes.

Improved tolerance to salt and water stress in Drosophila melanogaster cells conferred by late embryogenesis abundant protein

“…Several LEA proteins belonging to groups 3 and 4 are predicted to reside in mitochondria of the plant Arabidopsis thaliana (Hundertmark and Hincha, 2008). Furthermore, a group 3 LEA protein from pea seeds (PsLEAm) is imported into the mitochondrial matrix and protects mitochondrial matrix enzymes from activity loss and artificial liposomes from vesicle fusion during in vitro desiccation experiments (Grelet et al, 2005;Tolleter et al, 2010;Tolleter et al, 2007). Anhydrobiotic animals apparently have developed similar strategies to survive water loss; multiple LEA proteins belonging to groups 1 and 3 are present in mitochondria of A. franciscana embryos (Menze et al, 2009;Warner et al, 2010).…”

“…Additionally, the repeating motifs of group 1 proteins consist of 20 amino acids, while group 3 proteins are characterized by 11-mer motifs (Battaglia et al, 2008). Mitochondrial targeted LEA proteins may help to maintain the integrity and functionality of the organelle when water is scarce through interactions with proteins and membranes but the mechanisms by which protection is conferred are still unclear (Grelet et al, 2005;Menze et al, 2009;Stupnikova et al, 2006;Tolleter et al, 2010;Tolleter et al, 2007).…”

Tunable Membrane Binding of the Intrinsically Disordered Dehydrin Lti30, a Cold-Induced Plant Stress Protein

“…The ability of Lti30 to assemble synthetic vesicles and ex vivo membranes into large aggregates has not been reported before, but other LEA proteins have recently been shown to have similar ability (Bož ović , 2007;Hundertmark et al, 2011). However, the mitochondrial LEA protein LEAM has been observed to bind and stabilize lipid vesicles upon drying, but aggregation is not reported to accompany the process (Tolleter et al, 2007). Likewise, the membrane binding dehydrin DHN1 from maize seems to lack the ability to aggregate vesicles since circular dichroism (CD) spectra in the presence of vesicles could be monitored without disturbances, indicating well dispersed solutions (Soulages et al, 2003;Koag et al, 2009).…”

A Nuclear Gene Encoding the Iron-Sulfur Subunit of Mitochondrial Complex II Is Regulated by B3 Domain Transcription Factors during Seed Development in Arabidopsis

“…A similar pattern has been described only once for a mitochondrial protein, a pea (Pisum sativum) LEA protein. This protein may be involved in protecting the inner mitochondrial membrane during seed desiccation (Grellet et al, 2005;Tolleter et al, 2007); however, no data concerning the regulation of its expression are available. Here, we have performed a detailed characterization of the SDH2-3 promoter and identified key regulatory elements and transcription factors involved in its regula- tion.…”