In this issue

1479 Cleavage of cellulose by a CBM33 protein

Zarah Forsberg, Gustav Vaaje-Kolstad, Bjørge Westereng, Anne C. Bunæs, Yngve Stenstrøm, Alasdair MacKenzie, Morten Sørlie, Svein J. Horn, and Vincent G.H. Eijsink

The discovery of novel enzymes for the conversion of lignocellulosic biomass is of great biotechnological interest. Forsberg et al. describe such a novel enzyme, which is called CelS2 and classified as a CBM33 (Carbohydrate-Binding-Module 33). It is shown that CelS2 is a metal-dependent enzyme that cleaves crystalline cellulose, while oxidizing one of the newly generated chain ends. By doing so CelS2 boosts the activity of classical cellulases.

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1597 Computational design and selections for an engineered, thermostable terpene synthase

Juan E. Diaz, Chun-Shi Lin, Kazuyoshi Kunishiro, Birte K. Feld, Sara K. Avrantinis, Jonathan Bronson, John Greaves, Jeffery G. Saven, and Gregory A. Weiss

To date, terpenes comprise nearly half of all known natural products. The tremendous diversity of terpene structures ranges from simple, linear hydrocarbons to complex cyclic structures. Engineering terpene synthases for control over the synthesis of such compounds represents a long sought goal. Here, Diaz et al. report computational design, selection, and analysis of a thermostable mutant of the tobacco 5-epi-aristolochene synthase (TEAS) for the catalysis of carbocation cyclization reactions at elevated temperatures. The thermostable TEAS identified had roughly two times greater heat stability than the wild-type enzyme, remaining active up to 65 °C, whereas the wild-type enzyme lost activity at temperatures above 40 °C. Introducing mutations into the enzyme buttresses the protein against thermal denaturation; however, such stabilization decreases the catalytic activity of the enzyme. Thus, the reported study explores the complicated relationship between enzymatic thermodynamic stability and activity.

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1492 PLP-dependent enzymes as entry and exit gates of sphingolipid metabolism

Florence Bourquin, Guido Capitani, and Markus Gerhard Grütter

Sphingolipids are membrane constituents as well as extracellular and intracellular signaling molecules involved in many essential cellular processes. Two PLP dependent enzymes Serine-palmityol-transferase (SPT) and sphingosine-1-phosphate lyase (SPL) regulate the entry and exit gates of the sphingolipid metabolism. SPT catalyzes the condensation of serine and a fatty acid into 3-keto-dihydrosphingosine while SPL degrades sphingosine-1-phophate (S1P) into phosphoethanolamine and a long-chain aldehyde. An overview of the sphingolipid metabolism and of the recent biochemical and structural studies with prokaryotic SPT and SPL is provided in this article and the major similarities and differences to the corresponding eukaryotic enzymes are given. The important insight into the mechanism of action of these enzymes is discussed and a model of the way the eukaryotic enzymes are functioning at the surface of the membrane is presented. Since both enzymes are linked to severe diseases, they are potential targets for therapeutic intervention.

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1484 Crystal structure of New Delhi metallo-β-lactamase reveals molecular basis for antibiotic resistance

Dustin King and Natalie Strynadka

Recently in the clinic, the newly isolated New Delhi metallo-β-lactamase (NDM-1) has been found to confer Enterobacteriaceae with nearly complete resistance to β-lactam antibiotics including the widely prescribed penicillins and cephalosporins. The authors present the 2.1Å crystal structure of the apo form of NDM-1. This work reveals that NDM-1 has an enlarged active site cleft with a unique electrostatic profile, features which likely contribute to its broad-spectrum activity. Comparison of apo NDM-1 with the recently published product complex structure reveals key active site rearrangements that are induced upon substrate binding and product release. Taken together, this work provides unique structural insights that will be valuable for the design of NDM-1 inhibitors.

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