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The α-hemoglobin-stabilizing protein (AHSP), a small protein of 102 amino acids, is synthesized in red blood cell precursors. It binds specifically to α-hemoglobin (α-Hb) subunits acting as a chaperone protein, preventing the formation of α-hemoglobin-cytotoxic precipitates. We have engineered recombinant AHSP in a pGEX vector to study the functional consequence of interaction between AHSP and α-Hb. By in vitro binding assays, we have isolated the complexes glutathione S-transferase-AHSP·α-Hb and AHSP·α-Hb. The latter assembles as a heterodimer based on size-exclusion chromatography. These complexes exhibited monophasic CO binding kinetics, as observed for isolated α- and β-subunits of hemoglobin. However, the rate of CO (or oxygen) binding to α-hemoglobin bound to its chaperone is three times slower than that observed for isolated α-hemoglobin, demonstrating a form that is intermediate to the R- and T-hemoglobin states. The physiologically relevant replacement of the chaperone by β-hemoglobin chains could be detected by both ligand binding kinetics and tryptophan fluorescence quenching.

The 7-kDa lipid transfer proteins, LTP2s, share some amino-acid sequence similarities with the 9-kDa isoforms, LTP1s. Both proteins display an identical cysteine motif and, in this regard, LTP2s have been classified as lipid transfer proteins. However, in contrast with LTP1s, no data are available on their structure, cysteine pairings, lipid transfer and lipid binding properties. We reported on the isolation of two isoforms of 7-kDa lipid transfer protein, LTP2, from wheat seeds and showed for the first time that they indeed display lipid transfer activity. Trypsin and chymotrypsin digestions of the native LTP2 afforded the sequence of both isoforms and assignment of disulfide bonds. The cysteine pairings, Cys10–Cys24, Cys25–Cys60, Cys2–Cys34, Cys36–Cys67, revealed a mismatch at the Cys34-X-Cys36 motif of LTP2 compared to LTP1. Moreover, the secondary structure as determined by circular dichroism suggested an identical proportion of α helices, β sheets and random coils. By analogy with the structure of the LTP1, we discussed what structural changes are required to accommodate the LTP2 disulfide pattern.

The binding of two mono-acylated lipid monomers by plant lipid transfer proteins (LTP1s) presents an attractive field of research that could help our understanding of the functional role of this protein family. This task has been investigated in the case of barley LTP1 because it is known to exhibit a small cavity in its free state. The titration with lipids could not be followed by fluorescence with the native protein. Indeed, this LTP1 possesses a tyrosine residue on its C-terminus, Tyr91, which is not sensitive to lipid binding but mainly contributes to the fluorescence signal intensity. However, the binding of 1-myristoylglycerophosphatidylcholine (MyrGro-PCho) could be monitored by fluorescence after removal of Tyr91 by a carboxypeptidase. These experiments returned a dissociation constant of about 1 µm and showed that the protein can indeed bind two monomers. This result was corroborated by molecular modelling where the structure of the complex between barley LTP1 and MyrGro-PCho was derived from that determined in the case of wheat [Charvolin, D., Douliez, J.P., Marion, D., Cohen-addad, C. & Pebay-Peyroula, E. (1999) Eur. J. Biochem.264, 562–568.]. Results from isothermal titration calorimetry experiments indicated non-classic titration behaviour but also suggested that two lipids could be bound by the protein. Finally, barley LTP1 binds two ω-hydroxypalmitic acid, a compound found in the family of cutin monomers. The fact that the binding of two lipids could be related to the physiological role of this protein family is discussed.

International audience; Neuroglobin (Ngb) and the cellular prion protein (PrPc), proteins of unknown function in the nervous system, are known to be expressed in the retina and have been observed in different rat retinal cells. The retina is the site of the highest concentration for Ngb, a heme protein of similar size and conformation to myoglobin. In this study, we demonstrated by immunohistochemical analysis of retinal colocalization of Ngb and PrPc in the ganglion cell layer. Considering for these two a common protective role in relation to oxidative stress and a possible transient contact during migration of PrPc through the eye or upon neuronal degradation, we undertook in vitro studies of the interaction of the purified proteins. Mixing these two proteins leads to rapid aggregation, even at submicromolar concentrations. As observed with the use of dynamic light scattering, particles comprising both proteins evolve to hundreds of nanometers within several seconds, a first report showing that PrPc is able to form aggregates without major structural changes. The main effect would then appear to be a protein–protein interaction specific to the surface charge of the Ngb protein with PrPc Nterminal sequence. A dominant parameter is the solvent ionic force, which can significantly modify the final state of aggregation. PrPc, normally anchored to the cell membrane, is toxic in the cytoplasm, where Ngb is present; this could suggest an Ngb function of scavenging proteins capable of forming deleterious aggregates considering a charge complementarity in the complex.

Recently, this laboratory has isolated from barley and beer extract an isoform of lipid transfer protein (LTP1), which was not fully sequenced (Jégou, S.; Douliez, J. P.; Mollé, D.; Boivin, P.; Marion, D. J. Agric. Food Chem. 2000, 48, 5023--5029). It was named LTP1b and exhibited a molecular weight 294 Da higher than that of the known LTP1. This paper reports the finding of an LTP1 isoform in wheat that also exhibits an excess of 294 Da compared to the native protein. Amino acid sequencing, reduction and alkylation, and mass spectrometry showed that this new LTP1b possesses the same N-terminal sequence as the native LTP1, suggesting that the difference resides in the binding of an adduct which has a molecular weight of 294 Da. The aim of the present paper is to highlight various biophysical techniques that afford the identification of such an isoform-like LTP1 and to correlate this finding with other isoforms of LTP1 that were isolated from other plants but not fully sequenced.