The three-dimensional solution structure of Ace-AMP1, an antifungal protein extracted from onion seeds, was determined using 1H NMR spectroscopy and molecular modeling. This cationic protein contains 93 amino acid residues and four disulfide bridges. Its structure was determined from 1260 NOE-derived distance restraints and 173 dihedral restraints derived from NOEs and 3JCaHNH coupling constants. The global fold involves four helical segments connected by three loops and a C-terminal tail without regular secondary structures, except for a 3(10)-helix turn and a beta-turn. The most striking feature is the absence of any continuous cavity running through the whole molecule as found in recently determined structures of nonspecific transfer proteins extracted from wheat and maize seeds, although their global folds are very similar. Consistent with the absence of a cavity in the core of Ace-AMP1, it was found that this protein, in contrast to ns-LTPs, does not bind fluorescently labeled phospholipids in solution. On the other hand, Ace-AMP1 is able to interact with phospholipid membranes as shown by the release of carboxyfluorescein from the lumen of artificial liposomes and by the induction of alterations in fluorescence polarization of fluorescently labeled phospholipids embedded in artificial liposomes.
Two familial cases of progressive external ophthalmoplegia with involvement of pharyngeal and distal muscles are presented. 'Ragged-red' fibres were found in both cases. Excessive amounts of RNA, as evidenced by the acridine orange-induced fluorescence, were noted in many muscle fibres, mostly in the 'ragged-red' fibres. At the ultrastructural level, numerous mitochondrial changes with paracrystalline formations were noted. Those formations were observed in three forms and three-dimensional reconstruction is proposed which suggests that the paracrystalline formations consist of undulating parallel leaflets joined along the top of the undulations. Small transverse bridges between neighbouring cristae and between cristae and paracrystalline formations are also emphasized. All those mitochondrial abnormalities are thought to represent the morphological expression of a biochemical deficiency in the inner membrane. They are interpreted thus: firstly, the biochemical defect leads to a multiplication of the mitochondria with increase in their volume and proliferation of the cristae in order to improve energy production; secondly, bridges between the modified inner membranes induce attachment of the neighbouring cristae and result in paracrystalline formations.
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