Abstract
The cell envelope proteinase (CEP) of Lactococcus lactis is a large extracellular protease covalently linked to the peptidoglycan of the cell wall. Strains of L. lactis are typically auxotrophic for several amino acids and in order to grow to high cell densities in milk they need an extracellular protease. The structure of the entire CEP enzyme is difficult to determine experimentally due to the large size and due to the attachment to the cell surface. We here describe the use of a combination of structure prediction tools to create a structural model for the entire CEP enzyme of Lactococcus lactis. The model has implications for how the bacterium interacts with casein micelles during growth in milk, and it has implications regarding the energetics of the proteolytic system. Our model for the CEP indicates that the catalytic triad is activated through a structural change caused by interaction with the substrate. The CEP of L. lactis might become a useful model for the mode of action for enzymes belonging to the large class of S8 proteinases with a PA (protease associated) domain and a downstream fibronectin like domain.
Highlights
Lactic acid bacteria (LAB) are commonly found in ecological niches rich in nutrients
The proteolytic system of LAB consist of an extracellular proteinase, various transporters allowing peptides and amino acids to be imported into the cell, and a range of intracellular peptidases completing the hydrolysis of peptides into amino acids
In this paper we describe the development of a structural model of the PrtP enzyme starting from the amino acid sequence of PrtP from Lactococcus lactis MS22337, a strain isolated from spontaneously acidified camel milk
Summary
Lactic acid bacteria (LAB) are commonly found in ecological niches rich in nutrients. The adaption to nutrient rich environments has resulted in extensive genome reduction and fastidious growth requirements including the demand for multiple amino acids (Jensen and Hammer, 1993; Makarova et al, 2006; Gänzle, 2015). In nutrient rich environments LAB compete against other microorganisms by fast growth and rapid accumulation of lactic acid from carbohydrate fermentation. The demand for essential amino acids will typically lead to a depletion of low molecular weight peptides and free amino acids. Growth beyond this point requires protein hydrolysis (Juillard et al, 1995b; Vermeulen et al, 2005). The extracellular proteinase is typically a large serine proteinase attached to the cell envelope with a proteinase
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