Enzymes catalyzing asymmetric carboligation reactions typically show very high substrate specificity for their nucleophilic donor substrate components. Structure-guided engineering of the thermostable transketolase from Geobacillus stearothermophilus by directed in vitro evolution yielded new enzyme variants that are able to utilize pyruvate and higher aliphatic homologues as nucleophilic components for acyl transfer instead of the natural polyhydroxylated ketose phosphates or hydroxypyruvate. The single mutant H102T proved the best hit toward 3-methyl-2-oxobutyrate as donor, while the double variant H102L/H474S showed highest catalytic efficiency toward pyruvate as donor. The latter variant was able to complement the auxotrophic deficiency of Escherichia coli cells arising from a deletion of the dxs gene, which encodes for activity of the first committed step into the terpenoid biosynthesis, offering the chance to employ a growth selection test for further enzyme optimization.

Application of aldolases for the asymmetric synthesis of multifunctional chiral products is hampered by their reputed strict nucleophile (=aldol donor) specificity owing to a mechanistic requirement for creating a carbanion nucleophile in aqueous medium. Here we report that a minimalist engineering can extensively broaden the substrate scope of native D-fructose-6-phosphate aldolase (FSA) from Escherichia coli, for which hydroxyacetone is the most proficient substrate, to accept an unprecedented wide variety of alternative nucleophiles. By single-or double-space-generating mutations using simple conservative Leu to Ala replacement of active site residues, we found enzyme variants to efficiently convert larger ketols and bioisosteric ether components with up to seven skeletal atoms, including linear and branched-chain structures. All reactions occurred with full retention of the natural D-threo diastereospecificity. These FSA variants open new avenues toward the synthesis of novel product families that hitherto were inaccessible by biological catalysis.

Sialic acid-containing glycoconjugates at the cell surface are of high importance in carbohydrate-mediated recognition phenomena in physiological and pathological events, as well as in bacterial or viral infection. A key step in the enzymatic synthesis of natural sialoconjugates and functional synthetic analogues is the activation of sialic acids to cytidine 5'-monophosphate (CMP)-sialic acid intermediates catalyzed by CMP-sialic acid synthetase (CSS). Based on our recently developed aligned protein model of substrate binding and a simple colorimetric screening assay, we have engineered the CSS from Neisseria meningitidis by structure-guided site-specific saturation mutagenesis at positions 192/193 to generate enzymes with broadened substrate scope. Top hits, including the F192S/F193Y variant, display an improvement of up to 70-fold catalytic efficiency relative to wild-type CSS for the conversion of sterically demanding N-acyl modified sialic acid analogues, without compromising protein stability. Such significantly enhanced substrate capacity is a major step forward to realizing a generalized chemo-enzymatic strategy for the efficient preparation of neo-sialoconjugate libraries, demonstrated by the highly efficient, regio-and stereospecific synthesis of 2,6-sialyllactose analogues by enzymatic coupling to the highly substrate tolerant a2,6-sialyltransferase from Photobacterium leiognathi JT-SHIZ-145. Our results further document the unusual versatility of the N. meningitidis CSS and engineered variants for a common synthetic approach to sialoconjugates comprising a large diversity of natural and non-natural sialic acid forms without the need for post-synthetic enzymatic modification.

The ets-family transcription factor ETV6 (TEL) has been shown to be the target of a large number of balanced chromosomal translocations in various hematological malignancies and in some soft tissue tumors. Furthermore, ETV6 is essential for hematopoietic stem cell function. We identified ETV6 interacting proteins using the yeast two hybrid system. One of these proteins is the HIV Tat interacting protein (TIP60), a histone acetyltransferase (HAT) containing the highly conserved MYST domain. TIP60 functions as a corepressor of ETV6 in reporter gene assays. Fluorescently tagged ETV6 and TIP60 colocalize in the nucleus and an increase in nuclear localization of ETV6 was seen when TIP60 was cotransfected. ETV6 interacts with TIP60 through a 63 amino acids region located in the central domain of ETV6 between the pointed and the ets domain. The ETV6 interacting region of TIP60 mapped to the C2HC zinc finger of the TIP60 MYST domain. The interaction of TIP60 with full length ETV6 required an intact acetyltransferase domain of TIP60. Interestingly, the MYST domains of MOZ and MORF were also able to interact with portions of ETV6. These observations suggest that MYST domain HATs regulate ETV6 transcriptional activity and may therefore play critical roles in leukemogenesis and possibly in normal hematopoietic development.

Defined sialoglycoconjugates are important molecular probes for studying the role of sialylated glycans in biological systems. We show that the α2,3‐sialyltransferase from Photobacterium phosphoreum JT‐ISH‐467 (2,3SiaTpph) tolerates a very broad substrate scope for modifications in the sialic acid part, including bulky amide variation, C5/C9 substitution, and C5 stereoinversion. To reduce the enzyme's hydrolytic activity, which erodes the product yield, an extensive structure‐guided mutagenesis study identified three variants that show up to five times higher catalytic efficiency for sialyltransfer, up to ten times lower efficiency for substrate hydrolysis, and drastically reduced product hydrolysis. Variant 2,3SiaTpph (A151D) displayed the best performance overall in the synthesis of the GM3 trisaccharide (α2,3‐Neu5Ac‐Lac) from lactose in a one‐pot, two‐enzyme cascade. Our study demonstrates that several complementary solutions can be found to suppress the common problem of undesired hydrolysis activity of microbial GT80 sialyltransferases. The new enzymes are powerful catalysts for the synthesis of a wide variety of complex natural and new‐to‐nature sialoconjugates for biological studies.