Evidence for the regulatory role of the N-terminal helix of secretory phospholipase A(2) from studies on native and chimeric proteins.
The phospholipase A(2) (PLA(2)) enzymes are activated by binding to phospholipid membranes. Although the N-terminal alpha-helix of group I/II PLA(2)s plays an important role in the productive mode membrane binding of the enzymes, its role in the structural aspects of membrane-induced activation of PLA(2)s is not well understood. In order to elucidate membrane-induced conformational changes in the N-terminal helix and in the rest of the PLA(2), we have created semisynthetic human group IB PLA(2) in which the N-terminal decapeptide is joined with the (13)C-labeled fragment, as well as a chimeric protein containing the N-terminal decapeptide from human group IIA PLA(2) joined with a (13)C-labeled fragment of group IB PLA(2). Infrared spectral resolution of the unlabeled and (13)C-labeled segments suggests that the N-terminal helix of membrane-bound IB PLA(2) has a more rigid structure than the other helices. On the other hand, the overall structure of the chimeric PLA(2) is more rigid than that of the IB PLA(2), but the N-terminal helix is more flexible. A combination of homology modeling and polarized infrared spectroscopy provides the structure of membrane-bound chimeric PLA(2), which demonstrates remarkable similarity but also distinct differences compared with that of IB PLA(2). Correlation is delineated between structural and membrane binding properties of PLA(2)s and their N-terminal helices. Altogether, the data provide evidence that the N-terminal helix of group I/II PLA(2)s acts as a regulatory domain that mediates interfacial activation of these enzymes.
Qin
Shan
S
Biomolecular Science Center, University of Central Florida, Orlando, Florida 32826, USA.
Pande
Abhay H
AH
Nemec
Kathleen N
KN
He
Xiaomei
X
Tatulian
Suren A
SA
D001665:Binding Sites; D002462:Cell Membrane / Q000378:metabolism*; D002942:Circular Dichroism; D054501:Group II Phospholipases A2; D006801:Humans; D007527:Isoenzymes; D008563:Membrane Lipids / Q000378:metabolism; D010179:Pancreas / Q000201:enzymology*; D010741:Phospholipases A / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D010743:Phospholipids / Q000378:metabolism*; D015202:Protein Engineering; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D017550:Spectroscopy, Fourier Transform Infrared; D013329:Structure-Activity Relationship; D013816:Thermodynamics
D007527:Isoenzymes; D008563:Membrane Lipids; D010743:Phospholipids; D011993:Recombinant Fusion Proteins; D010741:Phospholipases A; D054501:Group II Phospholipases A2