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Oxysterols are oxygenated derivatives of cholesterol that have a number of biological effects and play a key role in the maintenance of the body cholesterol balance. In this study, we describe the cDNA sequences and genomic structures of the recently identified human oxysterol-binding protein (OSBP)-related protein (ORP) family (Laitinen, S. et al. 1999. J. Lipid Res. 40: 2204-2211). The family now includes 12 genes/proteins, which can be divided into six distinct subfamilies. The ORP have two major structural features: a highly conserved OSBP-type sterol-binding domain in the C-terminal half and a pleckstrin homology domain present in the N-terminal region of most family members. Several ORP genes are present in S. cerevisiae, D. melanogaster, and C. elegans, suggesting that the protein family has functions of fundamental importance in the eukaryotic kingdom. Analysis of ORP mRNA levels in unloaded or acetylated LDL-loaded human macrophages revealed that the expression of ORP genes was not significantly affected by the loading, with the exception of ORP6, which was up-regulated 2-fold. The present study summarizes the basic characteristics of the OSBP-related gene/protein family in humans, and provides tools for functional analysis of the encoded proteins.

Oxysterol binding protein (OSBP) is a cytosolic protein that undergoes ligand-induced binding to the Golgi apparatus and has been implicated in the regulation of cellular cholesterol metabolism. In the yeast Saccharomyces cerevisiae an OSBP homologue is involved in membrane trafficking through the Golgi complex. Prompted by the multitude of OSBP-related genes in the yeast genome, we carried out a search for human expressed sequence tags (ESTs) displaying homology to the sterol-binding domain of OSBP. This revealed a minimum of six novel OSBP-related proteins, designated ORP-1 to ORP-6. ORP cDNA probes were generated by reverse transcription-PCR from human liver mRNA, and used for Northern blot analysis of human tissue transcript panels. This verified that each of them represents a different gene product and showed that they display distinct tissue-specific expression patterns. The ORP-1 and -2 mRNA expression levels were similar to or higher than that of OSBP while the ORP-3 to -6 mRNAs were detected at lower levels in specific tissues. The most abundantly expressed new gene, ORP-1, was transcribed at strikingly high levels in the cortical areas of human brain and displayed sterol-regulated expression in a cultured human neuroblastoma cell line. This indicates that ORP-1 may play an important role in maintaining the sterol balance in cells of the central nervous system. Together with OSBP, the identified gene products constitute a novel human protein family that may provide a link between organellar sterol status and membrane dynamics.

A new intensity correlation phenomenon at gamma-ray wavelengths is described. The influence of detector size on correlation effects is analyzed quantitatively. It is shown that dedicated synchrotron radiation sources, such as the Mössbauer beam line at the ESRF, will have characteristics allowing experimental observations of the correlation phenomenon.

We show that the classical model widely employed for the field radiated by an excited Mössbauer nucleus predicts an enhanced rate of coincidences for two detectors. This contradicts our experiment. We discuss the limits of applicability of the classical field concept for various experimental conditions.

Transient effects in Mössbauer spectroscopy were generated by sweeping the frequency or switching the phase of recoilless gamma radiation. From a sinusoidal frequency sweep a separation of source and absorber contributions to the experimental linewidth was obtained. With phase switching exceptionally large effects were observed. The experimental results were obtained mainly using the Zn resonance.

Abstract: Time-gated Zn-67 spectra measured during phase switching transients are presented. Novel line shapes appear in time-gated measurements in good agreement with theoretical calculations based on the assumption of coherent phase modulation with well-defined amplitude.

Abstract: Transient Mssbauer experiments with57Fe are described. A time resolution of 0.7 ns is achieved with a BaF2 scintillator. Polar polyvinylidene fluoride film is shown to be well suited for producing fast mechanical modulation. Pulses of recoilless gamma radiation, of width ≈30 ns and heigth 3.5 times the Mssbauer absorption, are generated with stepwise source motion. The efficiency of transient methods in extracting Mssbauer data is demonstrated with sinusoidal motion.

Abstract: The enhancement of recoilless fraction (f factor) in restricted geometries is studied. The experiments were carried out using the119Sn resonance in SnCl4 molecules trapped in porous glass. A theoretical approach to explain the increase of thef factor is presented.