Fig 1.

Conjugation steps. Native PS6B (1,000 kDa) has its size reduced to 20 kDa by acid hydrolysis. Then, aldehyde groups are produced by oxidation of the PS molecule. This reactive group (aldehyde) reacts directly with amine groups on rPspA by reductive amination (the method applied in commercial vaccines) or with amine groups present in OCT. In the second case, the product, PS6B-OCT, is subsequently reacted with carboxyl groups on mPspA, intermediated by DMT-MM, to form the conjugate. In order to increase the specificity of conjugation with PS6B-OCT, PspA's lysine was previously modified with formaldehyde (mPspA).