微藻光合作用制氢——能源危机的最终出路?

微藻光合作用制氢是解决能源短缺问题的有效途径.本文介绍了微藻光合作用制氢的机理,包括蓝藻固氮酶和可逆氢酶产氢以及绿藻可逆氢酶产氢的机理.在分析光合制氢限制因素的基础上,指出筛选和构建高效放氢藻株是制氢的有效途径.然后介绍了“直接生物光解”、固氮酶放氢和“间接生物光解”等制氢方式.利用绿藻“间接生物光解”水制氢是一种最有发展潜力的制氢方式.本文最后展望了微藻光合制氢的前景.     

The diversity of FtsY‐lipid interactions

The bacterial signal recognition particle (SRP) receptor FtsY forms a complex with the SRP Ffh to target nascent polypeptide chains to the bacterial inner membrane. How FtsY interacts with lipids and associates to the membrane is unclear. Here, we show that vesicle binding leads to partial protection against proteolytic degradation and a change in secondary structure, which differs depending on whether the lipids are simple mixtures of zwitterionic and anionic lipids, mimics of Escherichia coli lipids, or lysolipids. Lipid binding alters the stability of FtsY. Thermal unfolding of FtsY in buffer shows two transitions, one occurring at ～60°C and the other at ～90°C. The thermal intermediate accumulating between 60 and 90°C has structural features in common with the state induced by binding to E. coli lipids. E. coli lipid extract induces a single transition around 70°C, anionic lipids have no effect while cooperative unfolding is completely removed in lysolipids. Thus, the lipid environment profoundly influences the dynamic properties of FtsY, leading to three different kinds of FtsY‐lipid interactions with different effects on structure, proteolytic protection, and stability, and is driven both by hydrophobic and electrostatic interactions. Trypsin digestion experiments highlight the central role of the N‐domain in lipid contacts, whereas the A‐ and G‐domains appear to play a more minor part. © 2010 Wiley Periodicals, Inc. Biopolymers 93: 595–606, 2010. This article was originally published online as an accepted preprint. The “Published Online” date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com     

Differences in specificity and catalytic efficiency between allozymes of esterase-4 from Drosophila mojavensis

A more than 10-fold difference in the specificity and catalytic efficiency for 1-naphthyl esters was measured between two allozymes of esterase-4 from Drosophila mojavensis. This difference is mainly caused by a difference in the affinity for the 1-naphthyl esters. The amino acid compositions of the allozymes are not significantly different, which means that the difference in primary structure is small. Small differences in primary structure generally do not result in such a large increase in catalytic efficiency and such a large shift in substrate specificity as was found in the present study.      

The Compact and Biologically Relevant Structure of Inter-α-inhibitor Is Maintained by the Chondroitin Sulfate Chain and Divalent Cations

Inter-α-inhibitor is a proteoglycan of unique structure. The protein consists of three subunits, heavy chain 1, heavy chain 2, and bikunin covalently joined by a chondroitin sulfate chain originating at Ser-10 of bikunin. Inter-α-inhibitor interacts with an inflammation-associated protein, tumor necrosis factor-inducible gene 6 protein, in the extracellular matrix. This interaction leads to transfer of the heavy chains from the chondroitin sulfate of inter-α-inhibitor to hyaluronan and consequently to matrix stabilization. Divalent cations and heavy chain 2 are essential co-factors in this transfer reaction. In the present study, we have investigated how divalent cations in concert with the chondroitin sulfate chain influence the structure and stability of inter-α-inhibitor. The results showed that Mg²⁺ or Mn²⁺, but not Ca²⁺, induced a conformational change in inter-α-inhibitor as evidenced by a decrease in the Stokes radius and a bikunin chondroitin sulfate-dependent increase of the thermodynamic stability. This structure was shown to be essential for the ability of inter-α-inhibitor to participate in extracellular matrix stabilization. In addition, the data revealed that bikunin was positioned adjacent to both heavy chains and that the two heavy chains also were in close proximity. The chondroitin sulfate chain interacted with all protein components and inter-α-inhibitor dissociated when it was degraded. Conventional purification protocols result in the removal of the Mg²⁺ found in plasma and because divalent cations influence the conformation and affect function it is important to consider this when characterizing the biological activity of inter-α-inhibitor.     

α2-Macroglobulin-like protein 1 can conjugate and inhibit proteases through their hydroxyl groups,because of an enhanced reactivity of its thiol ester

Proteins in the α-macroglobulin (αM) superfamily use thiol esters to form covalent conjugation products upon their proteolytic activation. αM protease inhibitors use theirs to conjugate proteases and preferentially react with primary amines (e.g. on lysine side chains), whereas those of αM complement components C3 and C4B have an increased hydroxyl reactivity that is conveyed by a conserved histidine residue and allows conjugation to cell surface glycans. Human α₂-macroglobulin–like protein 1 (A2ML1) is a monomeric protease inhibitor but has the hydroxyl reactivity–conveying histidine residue. Here, we have investigated the role of hydroxyl reactivity in a protease inhibitor by comparing recombinant WT A2ML1 and the A2ML1 H1084N mutant in which this histidine is removed. Both of A2ML1s'' thiol esters were reactive toward the amine substrate glycine, but only WT A2ML1 reacted with the hydroxyl substrate glycerol, demonstrating that His-1084 increases the hydroxyl reactivity of A2ML1''s thiol ester. Although both A2ML1s conjugated and inhibited thermolysin, His-1084 was required for the conjugation and inhibition of acetylated thermolysin, which lacks primary amines. Using MS, we identified an ester bond formed between a thermolysin serine residue and the A2ML1 thiol ester. These results demonstrate that a histidine-enhanced hydroxyl reactivity can contribute to protease inhibition by an αM protein. His-1084 did not improve A2ML1''s protease inhibition at pH 5, indicating that A2ML1''s hydroxyl reactivity is not an adaption to its acidic epidermal environment.