The bacterial pathogen Legionella pneumophila exploits host cell vesicle transport by transiently manipulating the activity of the small guanosine triphosphatase (GTPase) Rab1. The effector protein SidM recruits Rab1 to the Legionella-containing vacuole (LCV), where it activates Rab1 and then AMPylates it by covalently adding adenosine monophosphate (AMP). L. pneumophila GTPase-activating protein LepB inactivates Rab1 before its removal from LCVs. Because LepB cannot bind AMPylated Rab1, the molecular events leading to Rab1 inactivation are unknown. We found that the effector protein SidD from L. pneumophila catalyzed AMP release from Rab1, generating de-AMPylated Rab1 accessible for inactivation by LepB. L. pneumophila mutants lacking SidD were defective for Rab1 removal from LCVs, identifying SidD as the missing link connecting the processes of early Rab1 accumulation and subsequent Rab1 removal during infection.

Growth retardation as well as the development of Cushingoid features in adrenally insufficient patients treated with the currently accepted replacement dose of cortisol (33-41 mumol/day.m2; 12-15 mg/m2.day) prompted us to reevaluate the cortisol production rate (FPR) in normal subjects and patients with Cushing's syndrome, using a recently developed thermospray liquid chromatography-mass spectrometry method. The stable isotope [9,12,12-2H3]cortisol was infused continuously for 31 h at about 5% of the anticipated FPR. Blood samples were obtained at 20-min intervals for 24 h, spun, and pooled in 4-h groups. Tracer dilution in plasma was determined by liquid chromatography/mass spectrometry. The method was validated with controlled infusions in 6 patients with adrenal insufficiency. Results from 12 normal volunteers revealed a FPR of 27.3 +/- 7.5 mumol/day (9.9 +/- 2.7 mg/day) or 15.7 mumol/day.m2; 5.7 mg/m2. day). A previously unreported circadian variation in FPR was observed. Patients with Cushing's syndrome demonstrated unequivocal elevation of FPR and cortisol concentration correlated during each sample period in normal volunteers, indicating that cortisol secretion, rather than metabolism, is mainly responsible for changes in plasma cortisol. Our data suggest that the FPR in normal subjects may be lower than previously believed.

The recently developed MALDI TOF-TOF instrument yields relatively complex but interpretable fragmentation spectra. When coupled with a straightforward sequence extension algorithm, it is possible to develop complete peptide sequences de novo from the spectra. This approach has been applied to a set of peptides derived from typtic digestion of electrophoretically separated sea urchin egg membrane proteins. When directed to proteins that have been described previously, the results were in essential agreement with those obtained by conventional data base searching approaches, with certain important exceptions. The present method detected errors in published sequences and was able to develop sequences from peptides differing in mass by one dalton (Da). These results show both the power of the present approach and the need for using de novo methods more frequently than may be otherwise appreciated. (J Am Soc Mass Spectrom 2002, 13, 784 -791)

Two major glycolipids, which comprise Ϸ36% of the total lipid mass from Borrelia burgdorferi, the etiological agent of Lyme disease, were investigated. We determined the fatty acid type, sugar identity, anomeric configuration, and substituent type and position. The structures were identified as cholesteryl 6-O-acyl-␤-D-galactopyranoside (B. burgdorferi glycolipid 1, BbGL-I), and 1,2-di-O-acyl-3-O-␣-D-galactopyranosyl-sn-glycerol (BbGL-II). The major fatty acids were palmitate and oleate. The structures were corroborated by gas-liquid chromatography MS, matrix-assisted laser desorption͞ionization time-of-flight spectroscopy, fast atom bombardment MS, detailed NMR spectrometry, and metabolic labeling. This is a previously undescribed demonstration of a cholesteryl galactoside in bacteria. Lipopolysaccharide was not detected in B. burgdorferi. The two glycolipids have several properties suggesting they may function as lipopolysaccharide: both are main components of the bacterial membrane, surface exposed, and have a three-domain structure. BbGL-I elicited specific antibodies in mice and rabbits, and BbGL-II elicited antibodies that reacted with both glycolipids.T he etiological agent of Lyme disease, Borrelia burgdorferi, is transmitted to humans through the bite of Ixodes ticks. Lyme disease is a multisystem infection, which affects the skin, joints, nervous system, and heart (1). The licensed vaccine (LYMErix, SmithKline Beecham) contains recombinant lipidated OspA. Although lipopolysaccharide (LPS) has been identified in several spirochaetales, such as Leptospira (2) and Treponema (3), there is no evidence for the presence of LPS in Borrelia species (4).Two surface-exposed glycolipids identified in B. burgdorferi react with sera from Lyme disease patients (5-7). These immunoreactive glycolipids have been characterized as monogalactosyl diacylglycerolipids (8). It has been proposed that these glycolipids differ only in their fatty acid composition. We designated these glycolipids as B. burgdorferi glycolipid I (BbGL-I) and B. burgdorferi glycolipid II (BbGL-II). We show that although BbGL-II is a monogalactosyl diacylglycerol as reported (8), BbGL-I has the unique structure cholesteryl 6-O-acyl-␤-D-galactopyranoside. Experimental ProceduresOrganism and Growth Conditions. B. burgdorferi strains B31 (ATCC 35210), BL303 (courtesy of G. Wormser, Division of Infectious Diseases, New York Medical College, Valhalla) and N40 (courtesy of L. Bockenstedt, Department of Internal Medicine, Yale University School of Medicine, New Haven, CT) were cultivated in BSK-H medium (Sigma). Media were inoculated with 2% (vol͞vol) of a frozen culture and incubated statically at 37°C for 72 h to the mid-exponential growth phase. Cells were harvested by centrifugation at 12,000 ϫ g for 30 min, washed three times with cold PBS, and stored at Ϫ20°C.Lipid Extraction and Purification. Lipids were extracted from washed cells as described (9). The chloroform was removed, and the dried lipids (0.1-0.2 mg͞mg cell) dissolved in 1-2 ml of chlorofor...