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Lipoprotein (a) [Lp(a)] is characterized by an LDL-like composition in terms of lipids and apoB100, and by one copy of a unique glycoprotein, apo(a). The apo(a) structure is mainly based on the repetition of tandem kringle domains with high homology to plasminogen kringles 4 and 5. Among them, kringle IV type 2 (KIV-2) is present in a highly variable number of genetically encoded repeats, whose length is inversely related to Lp(a) plasma concentration and cardiovascular risk. Despite it being the major component of apo(a), the actual function of KIV-2 is still unclear. Here, we describe the first high-resolution crystallographic structure of this domain. It shows a general fold very similar to other KIV domains with high and intermediate affinity for the lysine analog, ε-aminocaproic acid. Interestingly, KIV-2 presents a lysine binding site (LBS) with a unique shape and charge distribution. KIV-2 affinity for predicted small molecule binders was found to be negligible in surface plasmon resonance experiments; and with the LBS being nonfunctional, we propose to rename it “pseudo-LBS”. Further investigation of the protein by computational small-molecule docking allowed us to identify a possible heparin-binding site away from the LBS, which was confirmed by specific reverse charge mutations abolishing heparin binding. This study opens new possibilities to define the pathogenesis of Lp(a)-related diseases and to facilitate the design of specific therapeutic drugs.

Two distinct extracellular lipases were obtained from Penicillium solitum194A, isolated from domestic compost, and Cladosporium cladosporioides194B, isolated from dairy wastewater. These alkaline enzymes had molecular masses of 42 and 30 kDa, respectively. The P. solitum194A lipase differed in mass from previously reported enzyme, indicating that it is a novel lipase, and indicating that penicillia can secrete lipase isoenzymes. The C. cladosporioideslipase was more active on esters of medium-chain acids, whereas the P. solitumlipase was more active on longer chained substrates. The C. cladosporioidesenzyme displayed higher thermal stability than the P. solitumlipase, preserving full activity up to 48 °C and showing a T50(10 min) of 60 °C. Their different catalytic properties and good protein stability should make these enzymes suitable for biotechnological applications. Furthermore, the combined use of these two fungal strains may prove to be valuable in lipid-rich waste management.