Brogioni Silvia, Stampler Johanna, Furtmüller Paul G, Feis Alessandro, Obinger Christian, Smulevich Giulietta
Dipartimento di Chimica, Università di Firenze, Via della Lastruccia 3, I-50019 Sesto Fiorentino (FI), Italy.
Biochim Biophys Acta. 2008 May;1784(5):843-9. doi: 10.1016/j.bbapap.2008.02.014. Epub 2008 Mar 5.
In all mammalian peroxidases, the heme is covalently attached to the protein via two ester linkages between conserved aspartate (Asp94) and glutamate residues (Glu242) and modified methyl groups on pyrrole rings A and C. Only myeloperoxidase has an additional sulfonium ion linkage between the sulfur atom of the conserved methionine 243 and the beta-carbon of the vinyl group on pyrrole ring A. Upon reduction from Fe(III) to Fe(II), lactoperoxidase (LPO) but not myeloperoxidase (MPO) is shown to adopt three distinct active site conformations which depend on pH and time. Comparative spectroscopic analysis (UV-Vis absorption and resonance Raman) of the ferrous forms of LPO, wild-type MPO and the variants Asp94Val, Glu242Gln, Met243Thr and Met243Val clearly demonstrate that a single, stable ferrous form of MPO is present only in those proteins which retain an intact sulfonium linkage. By contrast, both ferrous Met243Thr and Met243Val can assume two conformations. They resemble ferrous LPO, being five-coordinated high-spin species that are distinguished by the strength of the proximal Fe-histidine bond. This bond weakens with time or decreasing pH, as indicated by the Fe-histidine stretching bands.
在所有哺乳动物过氧化物酶中，血红素通过保守的天冬氨酸（Asp94）和谷氨酸残基（Glu242）之间的两个酯键以及吡咯环A和C上的修饰甲基与蛋白质共价连接。只有髓过氧化物酶在保守的甲硫氨酸243的硫原子与吡咯环A上乙烯基的β-碳之间存在一个额外的锍离子键。从Fe（III）还原为Fe（II）后，乳过氧化物酶（LPO）而非髓过氧化物酶（MPO）会呈现出三种不同的活性位点构象，这取决于pH值和时间。对LPO、野生型MPO以及变体Asp94Val、Glu242Gln、Met243Thr和Met243Val的亚铁形式进行的比较光谱分析（紫外可见吸收和共振拉曼）清楚地表明，只有那些保留完整锍键的蛋白质中才存在单一、稳定的MPO亚铁形式。相比之下，亚铁形式的Met243Thr和Met243Val都可以呈现两种构象。它们类似于亚铁形式的LPO，是五配位的高自旋物种，其区别在于近端铁-组氨酸键的强度。如铁-组氨酸伸缩带所示，该键会随着时间或pH值的降低而减弱。
