Targeting CD33+ acute myeloid leukemia with GLK-33, a lintuzumab-auristatin conjugate with a wide therapeutic window.

CD33 (Siglec-3) is a cell surface receptor expressed in approximately 90% of AML blasts, making it an attractive target for therapy of acute myeloid leukemia (AML). While previous CD33-targeting antibody-drug conjugates (ADCs) like gemtuzumab ozogamicin (GO, Mylotarg) have shown efficacy in AML treatment, they have suffered from toxicity and narrow therapeutic window. This study aimed to develop a novel ADC with improved tolerability and a wider therapeutic window. GLK-33 consists of the anti-CD33 antibody lintuzumab and eight mavg-MMAU auristatin linker-payloads per antibody. The experimental methods included testing in cell cultures, patient-derived samples, mouse xenograft models, and rat toxicology studies. GLK-33 exhibited remarkable efficacy in reducing cell viability within CD33-positive leukemia cell lines and primary AML samples. Notably, GLK-33 demonstrated anti-tumor activity at single dose as low as 300 µg/kg in mice, while maintaining tolerability at single dose of 20 - 30 mg/kg in rats. In contrast to both GO and lintuzumab vedotin, GLK-33 exhibited a wide therapeutic window and activity against multidrug-resistant cells. The development of GLK-33 addresses the limitations of previous ADCs, offering a wider therapeutic window, improved tolerability, and activity against drug-resistant leukemia cells. These findings encourage further exploration of GLK-33 in AML through clinical trials.

Trastuzumab-MMAU Antibody-Auristatin Conjugates: Valine-Glucoserine Linker with Stabilized Maleimide Conjugation Improves In Vivo Efficacy and Tolerability.

PURPOSE: Antibody-drug conjugates (ADCs) have shown impressive clinical activity with approval of many agents in hematological and solid tumors. However, challenges remain with both efficacy and safety of ADCs. This study describes novel trastuzumab-auristatin conjugates with the hydrophilic MMAE prodrug MMAU, and optimization of a glycopeptide linker leading to a wider therapeutic window. EXPERIMENTAL DESIGN: Trastuzumab was conjugated with auristatin payloads via a series of linkers using a stabilized maleimide handle. The ADCs were characterized in vitro and their relative in vivo anti-tumor efficacies were assessed in HER2+ xenograft models. Relative linker stabilities and the mechanism of linker cleavage were studied using in vitro assays. Toxicity and toxicokinetics of the best performing ADC were evaluated in cynomolgus monkey (cyno). RESULTS: The trastuzumab-MMAU ADC with stabilized glycopeptide linker showed maleimide stabilization and higher resistance to cleavage by serum and lysosomal enzymes compared to a valine-citrulline conjugated trastuzumab ADC (trastuzumab-vc-MMAE). A single dose of 1 or 2 mg/kg of trastuzumab-MMAU at drug-to-antibody ratios (DAR) of 8 and 4 respectively resulted in xenograft tumor growth inhibition, with superior efficacy to trastuzumab-vc-MMAE. Trastuzumab-MMAU DAR4 was tolerated at doses up to 12 mg/kg in cyno, which represents 2- to 4-fold higher dose than that observed with vedotin ADCs, and had increased terminal half-life and exposure. CONCLUSIONS: The optimized trastuzumab-MMAU ADC showed potent antitumor activity and was well tolerated with excellent pharmacokinetics in non-human primates, leading to a superior preclinical therapeutic window. The data supports potential utility of trastuzumab-MMAU for treatment of HER2+ tumors.

Addressing the Biochemical Foundations of a Glucose-Based "Trojan Horse"-Strategy to Boron Neutron Capture Therapy: From Chemical Synthesis to In Vitro Assessment.

Boron neutron capture therapy (BNCT) for cancer is on the rise worldwide due to recent developments of in-hospital neutron accelerators which are expected to revolutionize patient treatments. There is an urgent need for improved boron delivery agents, and herein we have focused on studying the biochemical foundations upon which a successful GLUT1-targeting strategy to BNCT could be based. By combining synthesis and molecular modeling with affinity and cytotoxicity studies, we unravel the mechanisms behind the considerable potential of appropriately designed glucoconjugates as boron delivery agents for BNCT. In addition to addressing the biochemical premises of the approach in detail, we report on a hit glucoconjugate which displays good cytocompatibility, aqueous solubility, high transporter affinity, and, crucially, an exceptional boron delivery capacity in the in vitro assessment thereby pointing toward the significant potential embedded in this approach.

Structure and Function of Bovine Whey Derived Oligosaccharides Showing Synbiotic Epithelial Barrier Protective Properties.

Commensal gut microbiota and probiotics have numerous effects on the host's metabolic and protective systems, which occur primarily through the intestinal epithelial cell interface. Prebiotics, like galacto-oligosaccharides (GOS) are widely used to modulate their function and abundance. However, important structure-function relations may exist, requiring a detailed structural characterization. Here, we detailed the structural characterization of bovine whey derived oligosaccharide preparations enriched with GOS or not, dubbed GOS-enriched milk oligosaccharides (GMOS) or MOS, respectively. We explore GMOS's and MOS's potential to improve intestinal epithelial barrier function, assessed in a model based on barrier disruptive effects of the Clostridioides difficile toxin A. GMOS and MOS contain mainly GOS species composed of ß1-6- and ß1-3-linked galactoses, and 3'- and 6'-sialyllactose. Both GMOS and MOS, combined with lactobacilli, like Lactobacillus rhamnosus (LPR, NCC4007), gave synergistic epithelial barrier protection, while no such effect was observed with Bifidobacterium longum (BL NCC3001), Escherichia coli (Nissle) or fructo-oligosaccharides. Mechanistically, for barrier protection with MOS, (i) viable LPR was required, (ii) acidification of growth medium was not enough, (iii) LPR did not directly neutralize toxin A, and (iv) physical proximity of LPR with the intestinal epithelial cells was necessary. This is the first study, highlighting the importance of structure-function specificity and the necessity of the simultaneous presence of prebiotic, probiotic and host cell interactions required for a biological effect.

Identification and structural characterization of LytU, a unique peptidoglycan endopeptidase from the lysostaphin family.

We introduce LytU, a short member of the lysostaphin family of zinc-dependent pentaglycine endopeptidases. It is a potential antimicrobial agent for S. aureus infections and its gene transcription is highly upregulated upon antibiotic treatments along with other genes involved in cell wall synthesis. We found this enzyme to be responsible for the opening of the cell wall peptidoglycan layer during cell divisions in S. aureus. LytU is anchored in the plasma membrane with the active part residing in the periplasmic space. It has a unique Ile/Lys insertion at position 151 that resides in the catalytic site-neighbouring loop and is vital for the enzymatic activity but not affecting the overall structure common to the lysostaphin family. Purified LytU lyses S. aureus cells and cleaves pentaglycine, a reaction conveniently monitored by NMR spectroscopy. Substituting the cofactor zinc ion with a copper or cobalt ion remarkably increases the rate of pentaglycine cleavage. NMR and isothermal titration calorimetry further reveal that, uniquely for its family, LytU is able to bind a second zinc ion which is coordinated by catalytic histidines and is therefore inhibitory. The pH-dependence and high affinity of binding carry further physiological implications.

1H, 13C and 15N resonance assignments of the new lysostaphin family endopeptidase catalytic domain from Staphylococcus aureus.

Lysostaphin family endopeptidases, produced by Staphylococcus genus, are zinc-dependent enzymes that cleave pentaglycine bridges of cell wall peptidoglycan. They act as autolysins to maintain cell wall metabolism or as toxins and weapons against competing strains. Consequently, these enzymes are compelling targets for new drugs as well as are potential antimicrobial agents themselves against Staphylococcus pathogens, which depend on cell wall to retain their immunity against antibiotics. The rapid spread of methicillin and vancomycin-resistant Staphylococcus aureus strains draws demand for new therapeutic approaches. S. aureus gene sa0205 was found to be implicated in resistance to vancomycin and synthesis of the bacteria cell wall. The gene encodes for a catalytic domain of a lysostaphin-type endopeptidase. We aim to obtain the structure of the Sa0205 catalytic domain, the first solution structure of the catalytic domain of the lysostaphin family enzymes. In addition, we are to investigate the apparent binding of the second zinc ion, which has not been previously reported for the enzyme group. Herein, we present the backbone and side chain resonance assignments of Sa0205 endopeptidase catalytic domain in its one and two zinc-bound forms.

Structural Basis of the High Affinity Interaction between the Alphavirus Nonstructural Protein-3 (nsP3) and the SH3 Domain of Amphiphysin-2.

We show that a peptide from Chikungunya virus nsP3 protein spanning residues 1728-1744 binds the amphiphysin-2 (BIN1) Src homology-3 (SH3) domain with an unusually high affinity (Kd 24 nm). Our NMR solution complex structure together with isothermal titration calorimetry data on several related viral and cellular peptide ligands reveal that this exceptional affinity originates from interactions between multiple basic residues in the target peptide and the extensive negatively charged binding surface of amphiphysin-2 SH3. Remarkably, these arginines show no fixed conformation in the complex structure, indicating that a transient or fluctuating polyelectrostatic interaction accounts for this affinity. Thus, via optimization of such dynamic electrostatic forces, viral peptides have evolved a superior binding affinity for amphiphysin-2 SH3 compared with typical cellular ligands, such as dynamin, thereby enabling hijacking of amphiphysin-2 SH3-regulated host cell processes by these viruses. Moreover, our data show that the previously described consensus sequence PXRPXR for amphiphysin SH3 ligands is inaccurate and instead define it as an extended Class II binding motif PXXPXRpXR, where additional positive charges between the two constant arginine residues can give rise to extraordinary high SH3 binding affinity.

Hassallidins, antifungal glycolipopeptides, are widespread among cyanobacteria and are the end-product of a nonribosomal pathway.

Cyanobacteria produce a wide variety of cyclic peptides, including the widespread hepatotoxins microcystins and nodularins. Another class of peptides, cyclic glycosylated lipopeptides called hassallidins, show antifungal activity. Previously, two hassallidins (A and B) were reported from an epilithic cyanobacterium Hassallia sp. and found to be active against opportunistic human pathogenic fungi. Bioinformatic analysis of the Anabaena sp. 90 genome identified a 59-kb cryptic inactive nonribosomal peptide synthetase gene cluster proposed to be responsible for hassallidin biosynthesis. Here we describe the hassallidin biosynthetic pathway from Anabaena sp. SYKE748A, as well as the large chemical variation and common occurrence of hassallidins in filamentous cyanobacteria. Analysis demonstrated that 20 strains of the genus Anabaena carry hassallidin synthetase genes and produce a multitude of hassallidin variants that exhibit activity against Candida albicans. The compounds discovered here were distinct from previously reported hassallidins A and B. The IC50 of hassallidin D was 0.29-1.0 µM against Candida strains. A large variation in amino acids, sugars, their degree of acetylation, and fatty acid side chain length was detected. In addition, hassallidins were detected in other cyanobacteria including Aphanizomenon, Cylindrospermopsis raciborskii, Nostoc, and Tolypothrix. These compounds may protect some of the most important bloom-forming and globally distributed cyanobacteria against attacks by parasitic fungi.

New structural variants of aeruginosin produced by the toxic bloom forming cyanobacterium Nodularia spumigena.

Nodularia spumigena is a filamentous diazotrophic cyanobacterium that forms blooms in brackish water bodies. This cyanobacterium produces linear and cyclic peptide protease inhibitors which are thought to be part of a chemical defense against grazers. Here we show that N. spumigena produces structurally novel members of the aeruginosin family of serine protease inhibitors. Extensive chemical analyses including NMR demonstrated that the aeruginosins are comprised of an N-terminal short fatty acid chain, L-Tyr, L-Choi and L-argininal and in some cases pentose sugar. The genome of N. spumigena CCY9414 contains a compact 18-kb aeruginosin gene cluster encoding a peptide synthetase with a reductive release mechanism which offloads the aeruginosins as reactive peptide aldehydes. Analysis of the aeruginosin and spumigin gene clusters revealed two different strategies for the incorporation of N-terminal protecting carboxylic acids. These results demonstrate that strains of N. spumigena produce aeruginosins and spumigins, two families of structurally similar linear peptide aldehydes using separate peptide synthetases. The aeruginosins were chemically diverse and we found 11 structural variants in 16 strains from the Baltic Sea and Australia. Our findings broaden the known structural diversity of the aeruginosin peptide family to include peptides with rare N-terminal short chain (C2-C10) fatty acid moieties.

Enterohaemorrhagic Escherichia coli exploits a tryptophan switch to hijack host f-actin assembly.

Intrinsically disordered protein (IDP)-mediated interactions are often characterized by low affinity but high specificity. These traits are essential in signaling and regulation that require reversibility. Enterohaemorrhagic Escherichia coli (EHEC) exploit this situation by commandeering host cytoskeletal signaling to stimulate actin assembly beneath bound bacteria, generating "pedestals" that promote intestinal colonization. EHEC translocates two proteins, EspF(U) and Tir, which form a complex with the host protein IRTKS. The interaction of this complex with N-WASP triggers localized actin polymerization. We show that EspF(U) is an IDP that contains a transiently α-helical N-terminus and dynamic C-terminus. Our structure shows that single EspF(U) repeat forms a high-affinity trimolecular complex with N-WASP and IRTKS. We demonstrate that bacterial and cellular ligands interact with IRTKS SH3 in a similar fashion, but the bacterial protein has evolved to outcompete cellular targets by utilizing a tryptophan switch that offers superior binding affinity enabling EHEC-induced pedestal formation.

Diversity in prokaryotic glycosylation: an archaeal-derived N-linked glycan contains legionaminic acid.

VP4, the major structural protein of the haloarchaeal pleomorphic virus, HRPV-1, is glycosylated. To define the glycan structure attached to this protein, oligosaccharides released by ß-elimination were analysed by mass spectrometry and nuclear magnetic resonance spectroscopy. Such analyses showed that the major VP4-derived glycan is a pentasaccharide comprising glucose, glucuronic acid, mannose, sulphated glucuronic acid and a terminal 5-N-formyl-legionaminic acid residue. This is the first observation of legionaminic acid, a sialic acid-like sugar, in an archaeal-derived glycan structure. The importance of this residue for viral infection was demonstrated upon incubation with N-acetylneuraminic acid, a similar monosaccharide. Such treatment reduced progeny virus production by half 4 h post infection. LC-ESI/MS analysis confirmed the presence of pentasaccharide precursors on two different VP4-derived peptides bearing the N-glycosylation signal, NTT. The same sites modified by the native host, Halorubrum sp. strain PV6, were also recognized by the Haloferax volcanii N-glycosylation apparatus, as determined by LC-ESI/MS of heterologously expressed VP4. Here, however, the N-linked pentasaccharide was the same as shown to decorate the S-layer glycoprotein in this species. Hence, N-glycosylation of the haloarchaeal viral protein, VP4, is host-specific. These results thus present additional examples of archaeal N-glycosylation diversity and show the ability of Archaea to modify heterologously expressed proteins.

Recognition of tandem PxxP motifs as a unique Src homology 3-binding mode triggers pathogen-driven actin assembly.

Src homology 3 (SH3) domains are globular protein interaction modules that regulate cell behavior. The classic SH3 ligand-binding site accommodates a hydrophobic PxxP motif and a positively charged specificity-determining residue. We have determined the NMR structure of insulin receptor tyrosine kinase substrate (IRTKS) SH3 domain in complex with a repeat from Escherichia coli-secreted protein F-like protein encoded on prophage U (EspF(U)), a translocated effector of enterohemorrhagic E. coli that commandeers the mammalian actin assembly machinery. EspF(U)-IRTKS interaction is among the highest affinity natural SH3 ligands. Our complex structure reveals a unique type of SH3 interaction based on recognition of tandem PxxP motifs in the ligand. Strikingly, the specificity pocket of IRTKS SH3 has evolved to accommodate a polyproline type II helical peptide analogously to docking of the canonical PxxP by the conserved IRTKS SH3 proline-binding pockets. This cooperative binding explains the high-affinity SH3 interaction and is required for EspF(U)-IRTKS interaction in mammalian cells as well as the formation of localized actin "pedestals" beneath bound bacteria. Importantly, tandem PxxP motifs are also found in mammalian ligands and have been shown to contribute to IRTKS SH3 recognition similarly.

Glucuronidation of racemic O-desmethyltramadol, the active metabolite of tramadol.

O-Desmethyltramadol, the active metabolite of analgesic tramadol, is metabolised through glucuronidation. The present study was conducted to identify the human UDP-glucuronosyltransferases (UGTs) that catalyse the glucuronidation of O-desmethyltramadol, a racemic mixture of 1R,2R- and 1S,2S-enantiomers. We developed a fast and selective liquid chromatography-mass spectrometry method to separate, analyse and quantify the diastereomeric phenolic O-glucuronides of O-desmethyltramadol. To quantify O-desmethyltramadol glucuronidation, we biosynthesised both phenolic O-glucuronides of O-desmethyltramadol and verified their structure by mass spectrometry and nuclear magnetic resonance spectroscopy. Subsequently, the 16 human UGTs of subfamilies 1A and 2B were screened for O-desmethyltramadol glucuronidation activity. UGTs 1A7-1A10 exhibited a strict stereoselectivity, exclusively glucuroniding the 1R,2R-enantiomer. Similar though not strict enantioselectivity was exhibited by UGT2B15. UGT2B7, on the other hand, glucuronidated both O-desmethyltramadol enantiomers, with slight preference for 1S,2S-O-desmethyltramadol. Enzyme kinetic parameters were determined for the most active UGTs, 1A8 and 2B7. The apparent K(m) or S(50) values were high: 1.2mM±0.23 for 1R,2R-O-desmethyltramadol with UGT1A8 and 1.84±1.2 and 4.6±2.0mM for 1S,2S- and 1R,2R-O-desmethyltramadol enantiomers with UGT2B7, respectively. Glucuronidation analyses of O-desmethyltramadol with human liver microsomes exhibited stereoselectivity, favouring the 1S,2S-O-desmethyltramadol over 1R,2R-O-desmethyltramadol and yielding 62.4 and 24.6pmol/mg/min, respectively. In intestinal microsomes, on the other hand, the two enantiomers were glucuronidated at similar rates, about 6pmol/mg/min. The results shed new light on both tramadol metabolism and the substrate selectivity of the human UGTs.

HA-detected experiments for the backbone assignment of intrinsically disordered proteins.

We propose a new alpha proton detection based approach for the sequential assignment of natively unfolded proteins. The proposed protocol superimposes on following features: HA-detection (1) enables assignment of natively unfolded proteins at any pH, i.e., it is not sensitive to rapid chemical exchange undergoing in natively unfolded proteins even at moderately high pH. (2) It allows straightforward assignment of proline-rich polypeptides without additional proline-customized experiments. (3) It offers more streamlined and less ambiguous assignment based on solely intraresidual (15)N(i)-(13)C'(i)-H(alpha)(i) (or (15)N(i)-(13)C(alpha)(i)-H(alpha)(i)) and sequential (15)N(i + 1)-(13)C'(i)-H(alpha)(i) (or (15)N(i + 1)-(13)C(alpha)(i)-H(alpha)(i)) correlation experiments together with efficient use of chemical shifts of (15)N and (13)C' nuclei, which show smaller dependence on residue type. We have tested the proposed protocol on two proteins, small globular 56-residue GB1, and highly disordered, proline-rich 47-residue fifth repeat of EspF(U). Using the proposed approach, we were able to assign 90% of (1)H(alpha), (13)C(alpha), (13)C', (15)N chemical shifts in EspF(U). We reckon that the HA-detection based strategy will be very useful in the assignment of natively unfolded proline-rich proteins or polypeptide chains.

HIV-1 Tat-peptide inhibits protein kinase C and protein kinase A through substrate competition.

HIV-1 Tat-peptide is widely used as a vector for cargo delivery into intact cells. As a cationic, arginine-rich peptide it can readily penetrate the plasma membrane and facilitate the penetration of impermeable bioactive molecules such as proteins, peptides, nucleic acids and drugs. Although at first considered as an inert vector, recent studies have however shown that it might have effects on its own on various cellular processes. In the present study we have investigated the effects of the Tat-peptide(48-60) on two basic serine/threonine kinases, protein kinase C and A, since earlier studies have shown that certain arginine-rich peptides or proteins might have a modulatory effect on their activity. In in vitro studies, Tat-peptide inhibited PKC alpha in a concentration-dependent manner with an IC(50)-value of 22nM and PKA with an IC(50)-value of 1.2 microM. The mode of inhibition was studied in the presence of increasing concentrations of a substrate peptide or ATP. Tat-peptide competed with the kinase substrates, however it did not compete with ATP. In a panel of 70 kinases Tat-peptide showed inhibitory activity at least towards other AGC-family kinases (PKB, SGK1, S6K1, MSK1), CAMK-family kinases (CAMK1 and MELK) and a STE family kinase (MKK1). In HeLa cells Tat-peptide inhibited the phorbol ester-evoked ERK1/2 phosphorylation suggesting that Tat inhibited PKC also in intact cells. In thyroid cells Tat-peptide attenuated sphingosylphosphorylcholine-evoked Ca(2+)-fluxes, which have earlier been shown to be dependent on PKC. Taken together, these results indicate that the Tat-peptide(48-60) is a potent inhibitor which binds to the substrate binding site of the basophilic kinase domain.

The N-glycome of human embryonic stem cells.

BACKGROUND: Complex carbohydrate structures, glycans, are essential components of glycoproteins, glycolipids, and proteoglycans. While individual glycan structures including the SSEA and Tra antigens are already used to define undifferentiated human embryonic stem cells (hESC), the whole spectrum of stem cell glycans has remained unknown. We undertook a global study of the asparagine-linked glycoprotein glycans (N-glycans) of hESC and their differentiated progeny using MALDI-TOF mass spectrometric and NMR spectroscopic profiling. Structural analyses were performed by specific glycosidase enzymes and mass spectrometric fragmentation analyses. RESULTS: The data demonstrated that hESC have a characteristic N-glycome which consists of both a constant part and a variable part that changes during hESC differentiation. hESC-associated N-glycans were downregulated and new structures emerged in the differentiated cells. Previously mouse embryonic stem cells have been associated with complex fucosylation by use of SSEA-1 antibody. In the present study we found that complex fucosylation was the most characteristic glycosylation feature also in undifferentiated hESC. The most abundant complex fucosylated structures were Lex and H type 2 antennae in sialylated complex-type N-glycans. CONCLUSION: The N-glycan phenotype of hESC was shown to reflect their differentiation stage. During differentiation, hESC-associated N-glycan features were replaced by differentiated cell-associated structures. The results indicated that hESC differentiation stage can be determined by direct analysis of the N-glycan profile. These results provide the first overview of the N-glycan profile of hESC and form the basis for future strategies to target stem cell glycans.

Design, synthesis, and biological activity of isophthalic acid derivatives targeted to the C1 domain of protein kinase C.

Protein kinase C (PKC) is a widely studied molecular target for the treatment of cancer and other diseases. We have approached the issue of modifying PKC function by targeting the C1 domain in the regulatory region of the enzyme. Using the X-ray crystal structure of the PKC delta C1b domain, we have discovered conveniently synthesizable derivatives of dialkyl 5-(hydroxymethyl)isophthalate that can act as potential C1 domain ligands. Structure-activity studies confirmed that the important functional groups predicted by modeling were indispensable for binding to the C1 domain and that the modifications of these groups diminished binding. The most promising compounds were able to displace radiolabeled phorbol ester ([(3)H]PDBu) from PKC alpha and delta at K(i) values in the range of 200-900 nM. Furthermore, the active isophthalate derivatives could modify PKC activation in living cells either by inducing PKC-dependent ERK phosphorylation or by inhibiting phorbol-induced ERK phosphorylation. In conclusion, we report here, for the first time, that derivatives of isophthalic acid represent an attractive novel group of C1 domain ligands that can be used as research tools or further modified for potential drug development.

Synthesis, structure characterization, and enzyme screening of clenbuterol glucuronides.

Two clenbuterol O-glucuronide diastereomers were synthesized by the Koenigs-Knorr reaction. Structures and glucuronidation sites of the glucuronides were characterized by tandem mass spectrometry and nuclear magnetic resonance spectroscopy. The two diastereomers were used as standard compounds in studies of stereoselective glucuronidation of clenbuterol with liver microsomes from different species and with 15 human recombinant UDP-glucuronosyltransferases. In this study, chemical and enzymatic reactions produced only O-glucuronides of clenbuterol, although on the basis of the chemical structure of the aglycone, both O- and N-glucuronides of clenbuterol could be formed. Differences in the production of diastereomers of clenbuterol glucuronides were observed among liver microsomes from the various animals. Dog and bovine liver microsomes were significantly active, and also stereoselective, each producing only one but a different diastereomer. Liver microsomes from rabbit and rat were also rather actively glucuronidating clenbuterol, but human, pig, and moose liver microsomes produced only minor amounts of glucuronides. Human liver microsomes produced only one clenbuterol glucuronide diastereomer, and the same was true of the human UDP-glucuronosyltransferases that were active (formation of glucuronide: 1A9 > 1A10 >> 1A7). The marked differences in the stereoselective glucuronidation of clenbuterol show that UDP-glucuronosyltransferases in the livers of different animals do not have the same functions, activities, or distribution. This needs to be taken into account, particularly in toxicology testing.

Glycomics of bone marrow-derived mesenchymal stem cells can be used to evaluate their cellular differentiation stage.

Human mesenchymal stem cells (MSCs) are adult multipotent progenitor cells. They hold an enormous therapeutic potential, but at the moment there is little information on the properties of MSCs, including their surface structures. In the present study, we analyzed the mesenchymal stem cell glycome by using mass spectrometric profiling as well as a panel of glycan binding proteins. Structural verifications were obtained by nuclear magnetic resonance spectroscopy, mass spectrometric fragmentation, and glycosidase digestions. The MSC glycome was compared to the glycome of corresponding osteogenically differentiated cells. More than one hundred glycan signals were detected in mesenchymal stem cells and osteoblasts differentiated from them. The glycan profiles of MSCs and osteoblasts were consistently different in biological replicates, indicating that stem cells and osteoblasts have characteristic glycosylation features. Glycosylation features associated with MSCs rather than differentiated cells included high-mannose type N-glycans, linear poly-N-acetyllactosamine chains and alpha2-3-sialylation. Mesenchymal stem cells expressed SSEA-4 and sialyl Lewis x epitopes. Characteristic glycosylation features that appeared in differentiated osteoblasts included abundant sulfate ester modifications. The results show that glycosylation analysis can be used to evaluate MSC differentiation state.

Structural basis of PxxDY motif recognition in SH3 binding.

We have determined the solution structure of epidermal growth factor receptor pathway substrate 8 (Eps8) L1 Src homology 3 (SH3) domain in complex with the PPVPNPDYEPIR peptide from the CD3epsilon cytoplasmic tail. Our structure reveals the distinct structural features that account for the unusual specificity of the Eps8 family SH3 domains for ligands containing a PxxDY motif instead of canonical PxxP ligands. The CD3epsilon peptide binds Eps8L1 SH3 in a class II orientation, but neither adopts a polyproline II helical conformation nor engages the first proline-binding pocket of the SH3 ligand binding interface. Ile531 of Eps8L1 SH3, instead of Tyr or Phe residues typically found in this position in SH3 domains, renders this hydrophobic pocket smaller and nonoptimal for binding to conventional PxxP peptides. A positively charged arginine at position 512 in the n-Src loop of Eps8L1 SH3 plays a key role in PxxDY motif recognition by forming a salt bridge to D7 of the CD3epsilon peptide. In addition, our structural model suggests a hydrogen bond between the hydroxyl group of the aromatic ring of Y8 and the carboxyl group of E496, thus explaining the critical role of the PxxDY motif tyrosine residue in binding to Eps8 family SH3. These finding have direct implications also for understanding the atypical binding specificity of the amino-terminal SH3 of the Nck family proteins.