Simplify the following text for a Grade 7 native English-speaking person.
Original: It is the main component of connective tissue , and is the most abundant protein in mammals , making up about 25 % to 35 % of the whole-body protein content .
Simplified: It is the main component of connective tissue , and is the most abundant protein in mammals . It makes up about 25 % to 35 % of the whole-body protein content .