Sex differences in the relationships between macronutrients and all-cause mortality in individuals with metabolically unhealthy overweight/obesity.

This study investigates sex differences in the effects of macronutrient quantity, quality, and timing on mortality in metabolically unhealthy overweight/obesity (MUO) populations. The study included 18,345 participants, including 9204 men and 9141 women. The Cox proportional risk model and isocaloric substitution effects were used to examine the association of macronutrient intake and subtype with all-cause mortality in the MUO populations. After adjusting for the potential covariates, The risk of all-cause mortality was elevated in men in the highest 25% percentile of poor-quality carbohydrates compared with men in the lowest quartile (odds ratio [OR]: 2.04; 95% confidence interval [CI], 1.40-2.98). Compared with women in the lowest quartile, the risk of all-cause mortality for women in the highest 25% percentile for high-quality carbohydrates (OR: 0.74; 95% CI, 0.55-0.99) and unsaturated fatty acids (OR: 0.54; 95% CI, 0.32-0.93) were decreased. In women, replacing low-quality carbohydrates with high-quality carbohydrates on an isocaloric basis reduces the risk of all-cause mortality by approximately 9%. We find that different macronutrient consumption subtypes are associated with all-cause mortality in MUO populations, with differential effects between men and women, and that the risk of all-cause mortality is influenced by macronutrient quality and meal timing.

Association between inflammatory biomarkers and mortality in individuals with type 2 diabetes: NHANES 2005-2018.

PURPOSE: This study aimed to examine independent association between inflammatory biomarkers and all-cause mortality as well as cardio-cerebrovascular disease (CCD) mortality among U.S. adults with diabetes. METHODS: A cohort of 6412 U.S. adults aged 20 or older was followed from the start until December 31, 2019. Statistical models such as Cox proportional hazards model (Cox) and Kaplan-Meier (K-M) survival curves were employed to investigate the associations between the inflammatory biomarkers and all-cause mortality and CCD mortality. RESULTS: After adjusting for confounding factors, the highest quartile of inflammatory biomarkers (NLR HR = 1.99; 95 % CI:1.54-2.57, MLR HR = 1.93; 95 % CI:1.46-2.54, SII HR = 1.49; 95 % CI:1.18-1.87, SIRI HR = 2.32; 95 % CI:1.81-2.96, nLPR HR = 2.05; 95 % CI:1.61-2.60, dNLR HR = 1.94; 95 % CI:1.51-2.49, AISI HR = 1.73; 95 % CI:1.4 1-2.12)) were positively associated with all-cause mortality compared to those in the lowest quartile. K-M survival curves indicated that participants with an inflammatory biomarker above a certain threshold had a higher risk of both all-cause mortality and CCD mortality (Log rank P < 0.05). CONCLUSION: Some biomarkers such as NLR, MLR, SII, AISI, SIRI, and dNLR, are significantly associated with all-cause mortality and CCD mortality among U.S. adults with diabetes. The risk of both outcomes increased when the biomarkers surpassed a specific threshold.

LC-MS-Guided Isolation of Cyanogripeptides A-C, Cyclolipopeptides with ß-Methyl-Leucine Residues, from an Actinoalloteichus cyanogriseus LHW52806.

Cyanogripeptides A-C (1-3), three new cyclolipopeptides with unusual ß-methyl-leucine residues, were identified from an Actinoalloteichus cyanogriseus LHW52806 using an LC-MS-guided strategy. The structures of compounds 1-3 were elucidated by 1D/2D NMR, HR-MS/MS, and the advanced Marfey's method. The absolute configuration of the ß-methyl-leucine residue was determined by a combination of stereoselective biosynthesis of (2S,3R)-ß-methyl-leucine, racemization to its epimer (2R,3R)-ß-methyl-leucine, and the advanced Marfey's method. The biosynthetic pathway of cyanogripeptides was deduced by analyzing the genome of A. cyanogriseus LHW52806. Compound 3 exhibited antibacterial activity against Helicobacter pylori G27, Helicobacter pylori 26695, and Mycolicibacterium smegmatis ATCC607 with MIC values of 32 µg/mL.

Depression status and insulin resistance in adults with obesity: A cross-sectional study.

OBJECTIVE: Insulin resistance (IR) frequently co-occurs with depression, but inconsistent associations between IR and depression have been reported, and less is known about the association in obesity, a major risk factor for both IR and depression. Thus the association between depression status and IR in a nationally representative sample of the US adults with obesity was evaluated. METHODS: This cross-sectional study involved 3507 adults with obesity from National Health and Nutrition Examination Survey from 2005 to 2016. The homeostasis model assessment of insulin resistance (HOMA-IR) was used, where IR was defined as a HOMA-IR value greater than its 75th percentile. The Patient Health Questionnaire 9 was used to assess the depression status. Multivariate logistic regression model was applied to evaluate the association between depression status and IR. RESULTS: The cut-off value of HOMA-IR in adults with obesity was 5.5, and the prevalence of IR was 26.3% in men, 19.8% in women. The association of depression status with IR depended upon gender (P for depression status by gender interaction = 0.04). Depression status was positively associated with IR in women (P = 0.01), where the ORs (95% CIs) for the risk of IR in the mild, moderate, severe depression status were 1.79 (1.21-2.64), 1.95 (1.10-3.45), and 2.21 (1.04-4.71), respectively (P for trend = 0.002). No association was found in men (P = 0.91). CONCLUSION: Positive association between IR and depression status was identified in women with obesity, where the risk of IR increased with the level of depression status, while no association was found in men with obesity.

Poor Uncorrected Visual Acuity and Association With Sleep Duration and Screen Time: A Dose-Response Relationship Study.

BACKGROUND: We aimed to investigate the prevalence of poor uncorrected visual acuity and the difference among students with different ages and residential areas in the Northeast of China. The relationships between screen time, nighttime sleep duration, and poor uncorrected visual acuity would be explored. METHODS: It was a cross-sectional study using multi-stage stratified random sampling method to recruit participants. 2149 students have completed questionnaires and underwent visual acuity examinations. The dose-response curve method was applied to examine the non-linear associations between sleep duration and poor uncorrected visual acuity under different screen time subgroups. RESULTS: The overall prevalence of poor uncorrected visual acuity and severe poor uncorrected visual acuity was 84.7% and 63.3%, respectively. The dose-response curve showed the odds ratios (ORs) of sleep duration for the poor uncorrected visual increased relatively slowly when screen time <1 hour, then increased dramatically in screen time ≥1 hours. The ORs of sleep time and poor uncorrected visual acuity showed a U-shaped change trend among students with 2 or more hours of screen time every day. CONCLUSION: We found associations between nighttime sleep duration and poor uncorrected visual acuity in adolescents. However, these associations were not consistent across all screen time categories.

The association between fatty acid intake and breast cancer based on the NHANES and Mendelian randomization study.

BACKGROUND: Observational studies have examined the association between fatty acid intake and breast cancer (BC), and the association might vary depending on menopausal status, but the results remain controversial. The objective of this study was to investigate the associations between fatty acid intake and BC. METHODS: The National Health and Nutrition Examination Survey (NHANES) 1999-2016 was used in the study, and stratified analysis by menopausal status was performed. Logistic regression models were used to evaluate the associations between BC and intake of saturated fatty acids (SFAs), monounsaturated fatty acids (MUFAs), and polyunsaturated fatty acids (PUFAs), adjusting for covariates. Three two-sample Mendelian randomization (MR) methods-inverse variance weighted (IVW), weighted median, and Mendelian randomization-Egger (MR-Egger) regression-were applied to further verify the associations between intake of fatty acids and BC. RESULTS: Higher intake of MUFAs was associated with lower risk of BC in premenopausal women: ORs (95 %CI): 0.325 (0.110, 0.964). IVW showed that increased intake of MUFAs was associated with a reduced risk of BC: 0.997 (0.995, 1.000), p = 0.024. No associations between BC and SFAs, MUFAs or PUFAs were found in postmenopausal women or in the overall population. CONCLUSIONS: Increasing intake of MUFAs might reduce the risk of BC in premenopausal women. The protective effect of MUFAs on BC was also supported by MR study.

Selection of mutant µplasmin for amyloid-ß cleavage in vivo.

One of the main culprits of Alzheimer's disease (AD) is the formation of toxic amyloid-ß (Aß) peptide polymers and the aggregation of Aß to form plaques in the brain. We have developed techniques to purify the catalytic domain of plasmin, micro-plasmin (µPlm), which can be used for an Aß-clearance based AD therapy. However, in serum, µPlm is irreversibly inhibited by its principal inhibitor α2-antiplasmin (α2-AP). In this study, we engineered and selected mutant forms of µPlm that are both catalytically active and insensitive to α2-AP inhibition. We identified surface residues of µPlm that might interact and bind α2-AP, and used an alanine-scanning mutagenesis method to select residues having higher activity but lower α2-AP inhibition. Then we employed saturation mutagenesis for further optimize both properties. Modeled complex structure of µPlm/α2-AP shows that F587 is a critical contact residue, which can be used as a starting position for further investigation.

Oxidation-resistant and thermostable forms of alpha-1 antitrypsin from Escherichia coli inclusion bodies.

Native α1-antitrypsin (AAT) is a 52-kDa glycoprotein that acts as an antiprotease and is the physiological inhibitor of neutrophil serine proteases. The main function of AAT is to protect the lung from proteolytic damage induced by inflammation. AAT deficiency (AATD) is a codominant autosomal disorder caused by pathogenic mutations in SERPINA1 gene, leading to reduced levels of serum AAT. The deficiency is known to increase the risk of pulmonary emphysema and chronic obstructive pulmonary disease as a consequence of proteolytic imbalance induced by inflammation, associated in many instances with cigarette smoking and other environmental hazards. Currently, the available therapy for lung disease associated with AATD is serum purified human AAT injected into patients on a weekly basis. It would be advantageous to replace serum-derived AAT with a recombinant version which is stable and resistant to oxidation. We have expressed AAT in Escherichia coli as inclusion bodies and developed a highly efficient refolding and purification process. We engineered a series of mutant forms of AAT to achieve enhance thermostability and oxidation resistance. Moreover, we synthesized an active form of AAT via cysteine-pegylation to achieve a markedly extended half-life in vivo. The resulting molecule, which retains comparable activity to the wild-type form, is expected to be an improved therapeutic agent for treating hereditary emphysema. In addition, the molecule may also be used to treat other types of emphysema caused by smoking, cystic fibrosis, pulmonary hypertension, pulmonary fibrosis, and chronic obstructive pulmonary disease.

Recovering organic matters and ions from wastewater by genetically engineered Bacillus subtilis biomass.

Water pollution causes substantial damage to the environment and to human health, and the current methods to treat pollution suffer from high cost and low efficiency, resulting in increased environmental damages. Using genetic modification and functional selection, we developed a novel biosorbent from Genetically Engineered Bacillus subtilis (GEBS) cells. At a ratio of biosorbent to direct blue dye of about 1:1.25 in a water solution, the dye pigments can be completely adsorbed in 40 s, decreasing COD to zero. Contrary to other biosorbents, ions such as Fe(2+) and Cu(2+) have significant advantages in terms of the adsorbing efficiency. The GEBS biomass can therefore capture both organics and ions from wastewater simultaneously and achieve co-precipitation in 2-10 min, which are features critical for practical applications of wastewater treatment. In addition, we used six different eluting solutions to regenerate used biomass, all resulting in renewed, highly efficient color and COD elimination capacities, with the best elution solution being NaHCO3 and Na2CO3. For practical applications, we showed a high COD elimination rate when using the GEBS biomass to treat raw water from textile enterprises, paper mill, and petrochemical industries. Compared with currently available adsorbing agents, the GEBS cells can adsorb organic and ion waste much faster and with much higher efficiency, can be regenerated and recycled efficiently, and may have broad applications in treating organic water pollution.

Recombinant GnRH-p53 protein sensitizes breast cancer cells to 5-fluorouracil-induced apoptosis in vitro and in vivo.

An ideal approach to treat cancers with dysfunctional p53 tumor suppressor gene is to reinstate p53 functionality by directly using p53 protein as a therapeutic agent. However, this has not been possible because the cells cannot readily internalize the protein. We constructed a fusion protein consisting of gonadotropin-releasing hormone (GnRH-p53) and p53 moieties. The recombinant protein was directly used to treat human breast cancer cells and athymic nude mice bearing breast cancer xenografts, with or without DNA synthesis-arresting agent 5-fluorouracil (5-FU). Treatments of cells from breast cancer cell-lines MDA-MB-231, T47D, or SKBR-3 with GnRH-p53 in combination with 5-FU significantly enhanced p53-activated apoptosis signals, including PUMA expression, BAX translocation to mitochondria, and activated caspase-3. Intratumoral injection of the GnRH-p53 protein inhibited MDA-MB-231 xenograft growth and induced p53-mediated apoptosis in the tumors. Systemic treatment of the tumor-bearing mice via tail vein injection of GnRH-p53 markedly augmented the anticancer efficacy of 5-FU. Substitution of GnRH-p53 with wild type p53 protein had no effect. Recombinant GnRH-p53 is able to function as a surrogate of p53 with regard to its apoptosis-inducing activity. Combination of GnRH-p53 with DNA-damaging drugs may be of important therapeutic value for cancer treatment.

Purification and characterization of mutant miniPlasmin for thrombolytic therapy.

BACKGROUND: Previous animal studies by us and others have indicated that catheter-administered plasmin or its des-kringle derivatives may be more appropriate alternatives to plasminogen activators for treating thrombolytic diseases, since it has a very short serum half-life and therefore does not result in hemorrhaging. We have previously produced recombinant miniPlasmin (mPlasmin) that was proven suitable for treating peripheral arterial occlusion in animal models. However, our previous results showed that non-specific cleavage at position K698 of mPlasmin during activation hindered the further development of this promising therapeutic candidate. In order to minimize or eliminate the non-specific cleavage problem, we performed saturation mutagenesis at the K698 position to develop a mutant form of mPlasmin for thrombolytic therapy. METHODS: We changed K698 to 16 other amino acids, with preferred E. coli codons. Each of these mutants were expressed in E. coli as inclusion bodies and then refolded, purified, and subsequently characterized by detailed kinetic assays/experiments/studies which identified highly active mutants devoid of non-specific cleavage. RESULTS: Activation studies indicated that at those conditions in which the wild type enzyme is cut at the non-specific position K698, the active mutants can be activated without being cleaved at this position. CONCLUSIONS: From the above results, we selected two mutants, K698Q and K698N, as our lead candidates for further thrombolytic drug developments. The selected mutants are potentially better therapeutic candidates for thrombolytic therapy.

The high pH and pH-shift refolding technology.

We have developed a high-pH, pH-shift refolding "Ph-Fold technology", both for academic research and industrial protein drug development applications. Using this technology, we were able to refold some "difficult-to-refold" proteins, some of which are proven important drug targets and protein drug candidates. The technology is composed of the initial E. coli production of inclusion bodies, the high pH solubilization/pH shift refolding screening technology, which includes automated pH shift refolding screening, and the methods of testing protein refolding without functional assay. This technology, especially the automated refolding system based on the Ph-Fold technology, may help both academic and industrial research in broadening structural genomic research, functional proteomics, and genomic scale drug development efforts.

Mercury distribution in neonatal rat brain after intrauterine methylmercury exposure.

Methylmercuric chloride (MMC) was orally administered to pregnant Wistar rats from gestational day 6 (G6) for 5 consecutive days. After delivery, the neonatal rats were decapitated and the cerebrum, cerebellum and hippocampus were excised on postnatal day (PND) 1, 7, 14, 21, 30 to determine total Hg contents and concentrations (six per stage). Both total Hg contents and concentrations in all the three regions increased as exposure dose increased and declined as postnatal time prolonged. Interestingly, differences of total Hg content between cerebrum and hippocampus at each time-point were significant (P<0.05). In the meantime, considering the Hg concentration, while no differences were observed before PND14 (P<0.05) among the three regions, Hg concentration in hippocampus was significantly higher than in cerebrum after that time period (P<0.05). We demonstrated that MeHg could pass through the placental and blood-brain barriers in a dose-dependent manner. Moreover, we found mercury redistribution occurred in offspring brain following the prolongation of postnatal time. The hippocampus was the major target of MeHg accumulation.

Recombinant, refolded tetrameric p53 and gonadotropin-releasing hormone-p53 slow proliferation and induce apoptosis in p53-deficient cancer cells.

The p53 tumor suppressor is mutated in over 50% of human cancers. Mutations resulting in amino acid changes within p53 result in a loss of activity and consequent changes in expression of genes that regulate DNA repair and cell cycle progression. Replacement of p53 using protein therapy would restore p53 function in p53-deficient tumor cells, with a consequence of tumor cell death and tumor regression. p53 functions in a tetrameric form in vivo. Here, we refolded a wild-type, full-length p53 from inclusion bodies expressed in Escherichia coli as a stable tetramer. The tetrameric p53 binds to p53-specific DNA and, when transformed into a p53-deficient cancer cell line, induced apoptosis of the transformed cells. Next, using the same expression and refolding technology, we produced a stable tetramer of recombinant gonadotropin-releasing hormone-p53 fusion protein (GnRH-p53), which traverses the plasma membrane, slows proliferation, and induces apoptosis in p53-deficient, GnRH-receptor-expressing cancer cell lines. In addition, we showed a time-dependent binding and internalization of GnRH-p53 to a receptor-expressing cell line. We conclude that the GnRH-p53 fusion strategy may provide a basis for constructing an effective cancer therapeutic for patients with tumors in GnRH-receptor-positive tissue types.

Refolding, purification, and activation of miniplasminogen and microplasminogen isolated from E. coli inclusion bodies.

Two des-kringle derivatives of human plasminogen, microplasminogen and miniplasminogen, have been expressed at high levels as inclusion bodies in Escherichia coli using a T7 expression system. In each case, the isolated inclusion bodies were refolded and purified. A final yield of approximately 10% of total refolded protein was observed in each case. Both refolded molecules were successfully activated to their functional forms, microplasmin and miniplasmin, by the plasminogen activator urokinase. The kinetic properties of the refolded microplasmin and miniplasmin were comparable to full length, native plasmin.

Maspin retards cell detachment via a novel interaction with the urokinase-type plasminogen activator/urokinase-type plasminogen activator receptor system.

It is well documented that tumor suppressive maspin inhibits tumor cell invasion and extracellular matrix remodeling. Maspin is a cytosolic, cell surface-associated, and secreted protein in the serine protease inhibitor superfamily. Although several molecules have been identified as candidate intracellular maspin targets, the extracellular maspin target(s) remains elusive. Although maspin does not directly inhibit urokinase-type plasminogen activator (uPA) activity, we have shown evidence that maspin may block the pericellular proteolysis mediated by cell surface-associated uPA. In the current study, maspin significantly inhibited the Ca2+ reduction-induced detachment of DU145 cells. This maspin effect was associated with increased and sustained levels of mature focal adhesion contacts (FAC). We noted that maspin (a) colocalized with uPA and uPA receptor (uPAR), (b) enhanced the interaction between uPAR and low-density lipoprotein receptor related protein, and (c) induced rapid internalization of uPA and uPAR. The maspin effects on surface-associated uPA and uPAR required the interaction between uPA and uPAR. Further biochemical and biophysical analyses revealed that maspin specifically bound to pro-uPA with a deduced K(d) of 270 nmol/L and inhibited the plasmin-mediated pro-uPA cleavage. Interestingly, substitution of maspin p1' site Arg340 in the reactive site loop (RSL) with alanine not only abolished the binding to pro-uPA but also diminished the maspin effects on pro-uPA cleavage and cell detachment. These data show an important role of maspin RSL in regulating the uPA/uPAR-dependent cell detachment. Together, our data led to a new hypothesis that maspin may stabilize mature FACs by quenching localized uPA/uPAR complex before uPA activation.

VEGI-192, a new isoform of TNFSF15, specifically eliminates tumor vascular endothelial cells and suppresses tumor growth.

PURPOSE: We determined the antiangiogenic and anticancer activity of VEGI-192, a new isoform of TNFSF15 (VEGI, TL1), with a Lewis lung cancer murine tumor model. EXPERIMENTAL DESIGN: Recombinant human VEGI-192 was produced in Escherichia coli and purified to apparent homogeneity. The protein was given systemically via i.p., i.v., or s.c. injections to tumor-bearing C57BL/6 mice. Tumor growth rates, animal survival rates, and general toxicity were determined. Effect on endothelial cell/smooth muscle cell ratio of the tumor vasculature was analyzed. RESULTS: Systemic administration of VEGI-192 gave rise to a marked inhibition of tumor growth. As much as 50% inhibition of the tumor growth rate was achieved with treatment initiated when the tumor volumes reached nearly 5% of the body weight. Inhibition of tumor formation was also observed when VEGI-192 was given at the time of tumor inoculation. Consistently, we observed an increased survival time of the treated animals. The VEGI-192-treated animals showed no liver or kidney toxicity. The treatment eliminated tumor endothelial cells but not vascular smooth muscle cells, which remained associated with a residual vascular structure consisting of the basement membrane. In addition, we carried out immunohistochemical analysis of rat kidneys and found that vascular endothelial cell growth inhibitor (VEGI) expression is largely limited to endothelial cells. CONCLUSIONS: Our findings indicate that VEGI is an endogenous inhibitor of angiogenesis, and that systemic administration of the VEGI-192 isoform resulted in inhibition of tumor angiogenesis and growth.

Enzymic properties of recombinant BACE2.

BACE2 (Memapsin 1) is a membrane-bound aspartic protease that is highly homologous with BACE1 (Memapsin 2). While BACE1 processes the amyloid precursor protein (APP) at a key step in generating the beta-amyloid peptide and presumably causes Alzheimer's disease (AD), BACE2 has not been demonstrated to be directly involved in APP processing, and its physiological functions remain to be determined. In vivo, BACE2 is expressed as a precursor protein containing pre-, pro-, protease, transmembrane, and cytosolic domains/peptides. To determine the enzymatic properties of BACE2, two variants of its pro-protease domain, pro-BACE2-T1 (PB2-T1) and pro-BACE2-T2 (PB2-T2), were constructed. They have been expressed in Escherichia coli as inclusion bodies, refolded and purified. These two recombinant proteins have the same N terminus but differ at their C-terminal ends: PB2-T1 ends at Pro466, on the boundary of the postulated transmembrane domain, and PB2-T2 ends at Ser431, close to the homologous ends of other aspartic proteases such as pepsin. While PB2-T1 shares similar substrate specificities with BACE1 and other 'general' aspartic proteases, the specificity of PB2-T2 is more constrained, apparently preferring to cleave at the NH2-terminal side of paired basic residues. Unlike other 'typical' aspartic proteases, which are active only under acidic conditions, the recombinant BACE2, PB2-T1, was active at a broad pH range. In addition, pro-BACE2 can be processed at its in vivo maturation site by BACE1.

A combined gene delivery by co-transduction of adenoviral and retroviral vectors for cancer gene therapy.

A novel second generation retroviral producer cell strategy (an adenoviral/retroviral combined delivery system) has been developed by this laboratory. In the present studies, this delivery system was used to examine its delivery efficiency in vitro and in vivo by using a marker gene, LacZ, and a therapeutic gene, herpes simplex virus thymidine kinase (HSV-tk), both of which were transduced into a tumor cell line KBALB. In the in vitro experiments for delivery efficacy of the LacZ gene, the delivery efficiency of KBALB+KBALBLNPOZAdN/H (1:1) was 27.8% higher than that of KBALB+KBALBLNPOZ (1:1) (P<0.01). For the antitumor effect of HSV-tk/ganciclovir (GCV), the death ratio of KBALB+KBALBLNCTKAdN/H (1:1) was higher than that of KBALB+KBALBLNCTK (1:1), on 4, 6, and 8 days at a concentration of 0.1, 1, and 10 microg/ml, respectively (P<0.01 or P<0.05). In the in vivo experiments for LacZ gene expression, the delivery efficiency in KBALB+KBALBLNPOZAdN/H (1:1) was 21.5% more efficient than that in KBALB+KBALBLNPOZ (1:1) (P<0.01). For HSV-tk/GCV antitumor effect, the suppression of tumors by KBALB+KBALBLNCTKAdN/H (1:1) was more effective than that by KBALB+KBALBLNCTK (1:1) (P<0.05). Results suggest that this new delivery system is more efficient than the traditional in vitro and in vivo retroviral vector delivery system.

The N-terminal 1000 residues of apolipoprotein B associate with microsomal triglyceride transfer protein to create a lipid transfer pocket required for lipoprotein assembly.

Apolipoprotein (apo) B, the major protein component of the atherogenic low-density lipoprotein (LDL), has a pentapartite structure, NH2-betaalpha1-beta1-alpha2-beta2-alpha3-COOH, the beta domains containing multiple amphipathic beta strands and the alpha domains containing multiple amphipathic alpha helixes. We recently reported that the first 1000 residues of human apoB-100 have sequence and amphipathic motif homologies to the lipid-pocket of lamprey lipovitellin (LV) [Segrest, J. P., Jones, M. K., and Dashti, N. (1999) J. Lipid Res. 40, 1401-1416]. The lipid-pocket of LV is a small triangular space lined by three antiparallel amphipathic beta sheets, betaA, betaB, and betaD. The betaA and betaB sheets are joined together by an antiparallel alpha helical bundle, alpha domain. We proposed [Segrest, J. P., Jones, M. K., and Dashti, N. (1999) J. Lipid Res. 40, 1401-1416] that formation of a LV-like lipid-pocket is necessary for lipid-transfer to apoB-containing lipoprotein particles and that this pocket is formed by association of the region of the betaalpha1 domain homologous to the betaA and betaB sheets of LV with a betaD-like amphipathic beta sheet from microsomal triglyceride transfer protein (MTP). To test this hypothesis, we generated four truncated cDNA constructs terminating at or near the juncture of the betaalpha1 and beta1 domains: Residues 1-800 (apoB:800), 1-931 (apoB:931), 1-1000 (apoB:1000), and 1-1200 (apoB:1200). Characterization of particles secreted by stable transformants of the McA-RH7777 cell line demonstrated that (i) ApoB:800, missing the betaB domain, was secreted as a lipid-poor aggregate. (ii) ApoB:931, containing most, but not all, of the betaB domain, was secreted as lipid-poor particles unassociated with MTP. (iii) ApoB:1000, containing the entire betaB domain, was secreted as a relatively lipid-rich particle associated hydrophobically with MTP. (iv) ApoB:1200, containing the betaalpha1 domain plus 200 residues of the beta1 domain, was secreted predominantly as a lipid-poor particle but also as a minor relatively lipid-rich, MTP-associated particle. We thus have captured an intermediate in apoB-containing particle assembly, a lipid transfer competent pocket formed by association of the complete betaalpha1 domain of apoB with MTP.