Role of Surface-Exposed Loops of Haemophilus influenzae Protein P2 in the Mitogen-Activated Protein Kinase Cascade
Authors: Domenica Capasso
Marina D&#x27;Isanto
Carlo Pedone
Stefania Galdiero
Massimiliano Galdiero
Mariateresa Vitiello
Journal: Infection and Immunity (2003)
Discipline: IMMUNOLOGY
Keywords: Gram-negative bacteria; porins; signal transduction pathways; Raf/MEK1-MEK2/mitogen-activated protein kinase (MAPK) cascade; P2 porin
Affiliations: Dipartimento di Chimica Biologica, Università degli Studi di Napoli Federico II and Istituto di Biostrutture e Bioimmagini, CNR, 80134 Naples, Italy., Dipartimento di Chimica Biologica, Università degli Studi di Napoli Federico II and Istituto di Biostrutture e Bioimmagini, CNR, 80134 Naples, Dipartimento di Patologia Generale, Dipartimento di Medicina Sperimentale, Facoltà di Medicina e Chirurgia, Seconda Università di Napoli, 80138 Naples, Italy

Abstract:  The outer membrane of gram-negative bacteria contains several proteins, and some of these proteins, the porins, have numerous biological functions in the interaction with the host; porins are involved in the activation of signal transduction pathways and, in particular, in the activation of the Raf/MEK1-MEK2/mitogen-activated protein kinase (MAPK) cascade. The P2 porin is the most abundant outer membrane protein of Haemophilus influenzae type b. A three-dimensional structural model for P2 was constructed based on the crystal structures of Klebsiella pneumoniae OmpK36 and Escherichia coli PhoE and OmpF. The protein was readily assembled into the beta-barrel fold characteristic of porins, despite the low sequence identity with the template proteins. The model provides information on the structural features of P2 and insights relevant for prediction of domains corresponding to surface-exposed loops, which could be involved in the activation of signal transduction pathways. To identify the role of surface-exposed loops, a set of synthetic peptides were synthesized according to the proposed model and were assayed for MEK1-MEK2/MAPK pathway activation. Our results show that synthetic peptides corresponding to surface loops of protein P2 are able to activate the MEK1-MEK2/MAPK pathways like the entire protein, while peptides modeled on internal beta strands are unable to induce significant phosphorylation of the MEK1-MEK2/MAPK pathways. In particular, the peptides corresponding to loops L5 (Lys206 to Gly219), L6B (Ser239 to Lys253), and L7 (Thr280 to Lys287) activate, as the whole protein, essentially JNK and p38. 

Retracted: No

PubPeer comments:
 My previuos comment got moderated, maybe it s because i didn t explain that the cut edge of the boxes indicates the orientation. So here s again: - **Figure 3**: There are some similar blots. Some of them need to be rotated to see the similarities. Note the different labels. ![file] , 
 Some more in the same figure. Since I had no more colours for the boxes I used the lines. The cut edge of the boxes and the position of the lines, indicate the orientation. ![file] , 
 Compare Figure 3 up here, with Figure 2 and 3 from this paper https: pubpeer.com publications A8765584CC85E943BCA5CB79901DAC#2, where Dr.Bik already highlighted some unexpected similarities. I added some boxes to Dr. Bik image, mantaining coerence with my previous comment, in order to highlight some similarities, but it became really messy, so I only left the ones on the Anti-p38 line. The reader will easily spot the other ones. ![file] ,